Ronald Reagan's "Morning in America" theme played well in 1984, when the economy was booming, jobs were plentiful, and Americans were "standing tall" in bars and boardrooms across the land.

But things are a bit different now. It may be morning in some parts of the country, but in regions heavily dependent on oil, textiles, mining, timber, and farming, it seems more like twilight. And should the have-nots express their economic frustrations at the polls, it could signal an end to the Reagan revolution and to the fundamental realignment of American politics that the Republicans have been talking so much about.

In this most political of months, all eyes are on the U.S. Senate, where the Republicans now enjoy a 53-47 majority, their first since 1954. Of the 34 Senate seats up for grabs this month, 22 are now held by Republicans, including 16 incumbents swept into office in the Reagan landslide of 1980. And of those 16, 14 hail from such economically troubled states as South Dakota, Idaho, Iowa, and Oklahoma. A loss of only 4 seats would put both houses of Congress in the hands of the Democrats and leave a lameduck President politically isolated.

For business, the stakes are enormously high. Although control of the Congress will not give Democrats a free hand in setting national policy -- the Democrats are almost as good at disagreeing with one another as they are with Republicans -- it will allow Democratic leaders to compete with Reagan in setting the national economic agenda. With an eye on the White House in '88, the Democrats would rush to hold a well-publicized series of oversight hearings, highlighting the failures of the Administration in cleaning up the environment, balancing the budget, and protecting American workers from uncaring employers and unfair foreign competition. In a Democratic Congress, Reagan initiatives could be more easily stalled or modified, and nominations to federal agencies more easily set aside.

In the House, the Democrats may increase their 71-seat majority, but their program will probably change very little. Much will depend on the new Speaker of the House, Jim Wright of Texas, whose political agenda is defined by the three Ps: populism, protectionism, and public works.

More dramatic would be the changes in the Senate, where even a bare Democratic majority would put ambitious and strong-willed liberals back in control of the Senate's powerful committee system. Here's a look at those Democratic chairmen-in-waiting, and a committee-by-committee look at what their return to power is likely to mean for American business.

COMMERCE, SCIENCE, AND TRANSPORTATION.

Missouri's John Danforth would hand over his gavel to Democrat Ernest "Fritz" Hollings of South Carolina, who has aspired at different times to be Senate majority leader and President and is always a viable Vice-Presidential possibility.

One immediate result of Hollings's chairmanship would be the almost certain death of product-liability reform, which Danforth was never able to steer through the Republican Senate. A trial lawyer by training and a states' righter by inclination, Hollings defends the authority of the 50 states to write their own liability statutes and the right of trial lawyers to bring whatever lawsuits they think are in their clients' best interests. Hollings is also an archfoe of the insurance industry, and he suspects it is the insurers, not the attorneys, who are responsible for any liability-insurance "crisis."

It is also the Commerce Committee that, under both Democrats and Republicans, has led the way on deregulation of the transportation industry -- railroads, airlines, and trucking. But Hollings, who has called himself a "born-again regulator," thinks it has all gone too far, particularly in aviation. The senator believes airlines are neglecting safety, engaging in damaging price wars on popular routes, and gouging passengers on noncompetitive small-city routes, such as those that take him home to his own Charleston, S.C. An aide, however, concedes that Hollings's inclination to reregulate will be held in check by fellow committee members from both parties, who might agree to adjustments to the policy of deregulation, but not to a wholesale retreat.

BANKING, HOUSING, AND URBAN AFFAIRS.

Wisconsin's William Proxmire used to be chairman, and he would probably be again, taking over from Utah's Jake Garn. Proxmire would inherit more than a committee, however. He'd inherit a hornet's nest.

The banking industry is in a period of rapid change. Bank failure rates in the South and West are escalating, while New York banks are sitting with billions in shaky overseas loans. Everywhere, big banks are looking to gobble up small banks within their own states and, where permitted, in neighboring states. At the same time, banks are also looking for permission to take even greater risks with depositors' money, moving into such sidelines as stock and insurance underwriting. One reason: competition from the growing number of unregulated nonbank banks, such as those run by American Express, J. C. Penney, and Travelers.

Many of the federal laws that govern all this date to the Great Depression, and everyone agrees that a thorough rewriting is long overdue. But there the agreement ends, as banks, insurance companies, investment bankers, and brokerage houses fight for advantage in the legislation that will define the ground rules for the brave new world of financial services. In the Senate, Garn has been pushing a massive bill that, among other things, would have opened the door to a free-for-all competition, a provision favored by the nation's big banks. But his efforts eventually collapsed under intense political pressure, and he was forced to put forward only two modest initiatives that left the central issues unresolved.

Proxmire, as chairman, would seek to slow the pace of deregulation, and perhaps even turn back the clock a bit. In general, he favors consumers and depositors over lenders, and small banks over big ones. He would permit banks to get into underwriting in the case of municipal bonds and mortgage-backed securities, but not riskier instruments such as stocks and junk bonds. And he would require regulators to keep a closer eye on bank reserves and portfolios, for the better protection of depositors. Proxmire would probably move quickly to close the regulatory loophole that created the nonbank banks. On interstate banking, he remains something of a skeptic.

JUDICIARY.

Hard-charging Joe Biden of Delaware, a man with Presidential ambitions, would replace South Carolina's Strom Thurmond. Although on the surface this might appear to be the most dramatic ideological shift should the Democrats take control, business lobbyists say Biden is a good listener, somebody they can work with.

Aside from judicial nominations, one area of likely controversy would be antitrust enforcement, which the Administration has all but abandoned. Biden would probably resurrect the Senate's antitrust subcommittee, naming Ohio's Howard Metzenbaum, a bombastic millionaire, as its chairman.

For his part, Metzenbaum would certainly hit the ground running. His nine-title revision of the antitrust laws has already been drafted, and it would sharply curb corporate mergers and acquisitions by establishing new criteria for Justice Department review. A Metzenbaum aide argues that "good antitrust laws are good for small business." But many business lobbyists are wary of anything that smacks of greater government control of private business decisions.

LABOR AND HUMAN RESOURCES.

The prospect that Edward Kennedy of Massachusetts might take over from Utah's Orrin Hatch as chairman of this committee has business lobbyists in something of a panic. Under Hatch, the committe has been hostile to labor interests, blocking several of labor's important legislative initiatives and making it harder for unions to organize workers. A Kennedy chairmanship would change all that. Admits John Motley, chief lobbyist for the National Federation of Independent Business: "We'd be on the defensive all the time."

One early battle could be over the Family and Medical Leave Act, which will probably clear the House next year. The bill would require that employers with more than 15 workers allow up to 18 weeks of unpaid leave to new parents and up to 26 weeks of unpaid sick leave to all employees -- all with uninterrupted health benefits and seniority and with jobs guaranteed upon return. To many business lobbyists, this is the camel's nose under the tent, the first of a long list of federally mandated fringe benefits, and they promise a major battle if a Democratic Senate attempts to take it up.

For a Democratic Senate, there is always the question of the minimum wage, which organized labor wants raised from $3.35 to $4.35 an hour.

Hoping to put the best foot forward with wary business interests, Kennedy's chief counsel on the committee predicts that a Kennedy-led committee would also take decisive steps to improve the nation's education system. "We want to improve the pool of trained manpower available to industry," says Thomas Rollins.

ENERGY AND NATURAL RESOURCES.

Louisiana's J. Bennett Johnston would take over from Republican James McClure of Idaho in a Democratic Senate -- presuming, that is, that Johnston loses his bid to replace Robert Byrd of West Virginia as Democratic leader of the Senate. In that case, seniority would probably catapult Dale Bumpers of Arkansas, a dark-horse Presidential aspirant, into the chair.

As on oil-state senator, Johnston, like McClure, favors decontrol of all natural-gas prices as well as development of energy reserves on federal lands. The two men part company, however, on the question of oil-import fees: McClure is against them, while Johnston would slap on a fee of $5 or more per barrel, both as a way of bolstering the domestic oil industry and helping to reduce the federal deficit.

The real hot potato for this committee next year, however, will concern the disposal of nuclear waste from power plants. Nuclear plants now produce about 1,500 metric tons of spent fuel each year, and already there are 12,000 tons of it sitting in cooling ponds at utility sites around the country, awaiting a final resting place. Congress thought it solved the problem back in 1982, directing the Energy Department to develop two deep-shaft repositories, one in the East, one in the West. But under political pressure, the Reagan Administration has stopped looking for the eastern site, sparking outrage out West. Now the entire effort is in doubt. In the past, Johnston has pushed the idea of retrievable ground-level storage facilities as a temporary solution. This is politically more palatable to more people -- economically more palatable, too: permanent disposal sites could cost up to $25 billion and be paid by consumers through utility-bill surcharges.

FINANCE.

Although Oregon's Bob Packwood has become something of a hero of the tax-reform effort this year, he is no hero with the business community, which estimates its tab for tax reform at about $120 billion a year. In a Democratic Senate, Packwood would give way to Lloyd Bentsen of Texas, a self-made millionaire known to lend a sympathetic ear to business interests.

Actually, it would be international trade issues, not tax issues, that would probably occupy center stage, with Democrats pushing for a major trade bill to close an expected trade deficit of $175 billion and protect jobs. One senator recently lambasted free-trade Reaganites who "talk like Rambo but act like Bambi" on international trade. Bentsen is more restrained in his criticism, but he is hardly a protectionist zealot. If there is one Democrat who can broker a compromise between free-trading Republicans and job-sensitive Democrats, it is probably Bentsen.

BUDGET.

Pete Domenici of New Mexico, the Republican chairman, has been saying for four years that no matter how many reductions are made in federal spending, new taxes will still be necessary to reduce a federal deficit reeling out of control. Lawton Chiles of Florida, the Democrat who would replace him, makes the point even more loudly. Chiles would probably force a confrontation on the issue with the President.

Take it all around, there's a lot on the line at the ballot box this month -- for the Democrats, for business, but most of all for President Reagan. While a lame-duck President usually gets very little from Congress during his last two years in office, a lame-duck President facing a Congress in the hands of the other party gets even less. At a time like that, Presidents often do what Presidents can: make speeches for the history books and concentrate on foreign policy.