Heading the "most wanted" list for millions of Americans (those of us old enough to feel our own mortality) is a simple, reliable way of financing the escalating costs of growing old.

The dream idea: A reverse mortgage, which allows you to tap the equity in your own home without being forced to sell the property.

So far, these loans have been more talked about than consummated. Only about 1,000 reverse mortgages have actually been written, estimates Ken Scholen, executive director of the National Center for Home Equity Conversion in Madison, Wis., and in many cases the home owner will eventually be forced to sell.

But finally, there's promise of real, and radical, change. The 1987 housing bill now before Congress includes a pilot program for lifetime reverse mortgages, to be run by the Department of Housing and Urban Development.

If passed -- and the outlook is good -- it could change the face of retirement across the country. Incomes could rise among the three-quarters of the elderly who own their homes. For older retirees, inflation would become less of a threat. More of the frail elderly could pay for health care in their own homes.

Here's how reverse mortgages work:

Assume that you own a house free and clear that's worth $80,000. A lender -- a bank or public agency -- might agree to lend you up to $64,000, usually at a fixed interest rate. But the money isn't paid to you all at once. Instead, you receive it in monthly installments -- in effect, creating regular tax-free income.

You make no ongoing payments on the loan. At the end of the term, however, all the interest and principal falls due at once. At that point, the house usually has to be sold to pay off the mortgage. The lender's fee may also include a portion of the appreciation on the property.

A few programs allow you to stay in the house for life.

Most require that the loan be repaid after a fixed number of years, usually no more than 10. (A fixed-term loan makes sense only for people who know they will have to move within that time -- perhaps because they're in poor health and expect to enter a nursing home.) The Virginia Housing Development Authority is exploring the idea of a reverse-mortgage credit line, so home owners can borrow as they need it, rather than on a fixed monthly schedule.

Reverse mortgages are available in 13 states, usually within limited geographical areas. For a list of the programs available, send a self-addressed, business-sized, stamped envelope to Scholen at NCHEC, 110 E. Main, Madison, Wis. 53703. Information is also available from the American Association of Retired Persons' Home Equity Information Center (1909 K St. NW, Washington, D.C. 20049).

But the business hasn't grown very much for three reasons: (1) Older home owners are rightly wary of loans that will eventually force them to sell their homes. (2) Lenders don't want to be in the position of evicting a 90-year-old who can't pay the money back. (3) A reverse mortgage that lasts for life is a high-risk enterprise for private lenders, especially as the loan cannot be sold to investors on the secondary market.

That's where the proposed federal pilot project comes in.

It will try insuring reverse mortgages through the Federal Housing Administration. Home owners will be able to stay put for life (or until they move out voluntarily); the government will guarantee their monthly payments, so they're protected if their lender goes bankrupt, and the Feds will guarantee the lender that he will get all his money back, even if the value of the house declines.

An insurance premium will be charged, probably paid by the borrower. (Details of the program, including who will offer it, will be developed through written regulations.) At death, or when the home owner moves, the house will be sold to repay the loan.

Congress envisions insuring up to 2,500 experimental loans over a four- to five-year period, in amounts ranging from $67,500 to $90,000, to home owners no younger than age 62. Assuming success, the program would expand and a secondary market would develop.

Three important points about the income you get from a reverse mortgage, as outlined by Scholen: It doesn't affect your eligibility for Social Security or Medicare.

It is classified as a loan, so it won't raise the taxes of Social Security beneficiaries.

In most states, it also won't affect your eligibility for SSI low-income payments or Medicaid, as long as you borrow only what you need to cover ongoing expenses. The bill in Congress requires that all the pros and cons be disclosed before anyone is allowed to sign up.