Imagine, for a moment, a revolving line of credit -- for yourself, not for your business. Imagine, too, that it is substantial, not limited by credit-card maximums or the value of your securities. And that it is cheap.

Too good to be true? Not if you own a house and happen to live in one of the eight states where Merrill Lynch & Co. has introduced its latest product.

Equity Access, as Merrill Lynch calls the new credit account, will provide you with cash up to 70% of the appraised value of your house, less any first mortgage balance. Once you are approved, the funds are yours for the asking for any period of time up to 10 years. The cost is two points over prime, considerably less than most consumer loans or second mortgages.

The only restriction -- and it is a legal one -- is that you can't use the money to purchase securities. (On the other hand, there is no law against using some other money to purchase securities.)

Introduced about a year and a half ago in California, Equity Access is now available to residents of Oregon, Connecticut Arizona, North Carolina, Virginia, Georgia, and Wisconsin as well. By late 1984, says Merrill Lynch Realty's Dennis Hess, it will be available in about 30 states.