A taxpayer, Ronald Reagan once said, is someone who works for the government -- but doesn't have to take a civil-service examination.

Certified public accountants aside, taxpayers also won't have to take an exam on the over-1,000-page tax act that Reagan signed into law last July. That's just as well: The Tax Reform Act of 1984, as it is known, contains hundreds of changes, revisions, and clarifications of the tax code (see INC., October, page 171). But, although you can leave the fine print to the professionals, you can't ignore the monster. Some of its provisions may well affect your return this year.

Where individual taxpayers are concerned, the most important new wrinkles relate to capital gains, divorces, income averaging, and tax shelters.

* Under the old law, income from the sale of assets couldn't be counted as long-term capital gains unless you owned the property for more than a year. Now, you have to hold on for only six months and a day to be eligible for the more favorable tax treatment. In general, short-term gains are fully taxable, whereas only 40% of long-term capital gains are taxable.

"This change will certainly make the stock market more attractive to investors," predicts Barry Hart, an attorney with the Washington, D.C., office of the international law firm Surrey & Morse. They will be able to take their profits sooner, without being locked into a stock for a full year." The law, however, applies only to assets acquired after June 22, 1984, and if you want to realize long-term gains on stocks purchased this year you have to watch your timing. A stock sold at a profit during the last week of December, points out Tom Drake, tax manager of the personal financial service group at Arthur Andersen & Co. in Chicago, will be recorded as 1985 income unless you specifically instruct your accountant to regard it as 1984 income.

* The act also makes the high cost of leaving less taxing. Under the old law divorcing spouses transferring property could be held responsible for capital-gains tax even though no cash was generated to pay the tax. The transferor, however, could not claim a loss if the property had declined in value. Now, in all cases, the spouse getting the property assumes liability for capital-gains taxes when the property is sold, and no gain or loss is recognized for tax purposes at the time of transfer. These changes apply to property transfers made after July 18, 1984 -- or, if both spouses elect, to transfers made after December 31, 1983.

As in the past, alimony is still deductible by the paying spouse and charged as income to the receiving spouse. But the new tax law spells out more clearly than in the past what does and does not qualify as alimony, and it requires alimony payers to provide the Internal Revenue Service with the name and Social Security number of the recipient. In the past, too, the parent with child custody usually claimed the $1,000 dependency exemption, but under certain circumstances the noncustodial parent could take the exemption instead. Now, the custodial parent always gets the exemption (provided custody is for the majority of the year) unless he or she waives the right.

* The new law has tightened the rules concerning income averaging. This is bad news to taxpayers who use this tactic to lessen their tax burden; Congress is hoping that this change alone will raise $2 billion annually. Before the change, you could profitably use income averaging if your current-year income was at least $3,000 higher than 120% of your average income for the previous four years. The new law, in effect for tax-year 1984 and thereafter, ups the percentage increase to 140%, and allows you to use only the past three years for the calculation.

* Congress is attempting to target and deter tax-shelter deals that let investors write off more money than they have it vested. As of this past August 31, sponsors of investments that allow write-off of 2:1 or more (and that meet certain other conditions) not only have to register the deal, but must also maintain lists of investors. The IRS hopes this new "scare tactic" will dissuade sponsors from pushing -- and investors from falling for -- deals designed solely for astronomical tax deductions.

Experts expect the IRS to take another cut at this change, however. The new guidelines "add confusion, not clarification," says Rick Talkov, tax manager with the Boston office of the accounting firm Laventhol & Horwath. "The rule is that any business set up with a 2:1 tax write-off has to register with the IRS. Any new venture that is being set up could have deductions that exceed the amount of cash put up."

There are other changes affecting investors in the legislation as well, but most of them are too complicated to explain in anything less than the multitude of pages the law itself takes up. These include rules concerning the time-value of money in calculating and reporting prepaid expenses and deductions for accrued expenses; rules relating to the 20% alternative minimum tax rate; and rules governing tax straddles, options, insurance annuities, and other investments. You may not need to read the new tax law in its relevant entirety -- but you should insist that your accountant, broker, or financial planner do so, just in case one of these provisions applies to you.

If they start reading now, they might be finished by the time tax season rolls around.