DEAR BOB: Several years ago we sold our old home and deferred paying our profit tax since we bought a more expensive house. If I should die with this tax unpaid, will my heirs have to pay it? Mark M., Bethesda.

DEAR MARK: No. The 1980 Oil Windfall Profits Tax Act, in a little noticed provision, stipulates that persons inheriting property receive it with a basis of its market value on the date of the decedent's death. It's called "stepped-up basis."

For example, suppose your adjusted cost basis of your home is $50,000 (including the deferred profit from the sale of your former principal residence). If your home is worth $95,000 on the date of your death, your heirs receive it at a $95,000 valuation. The deferred profit tax is forgiven by Uncle Sam.

If the heirs sell this home for $95,000, they pay no profit tax. But if they sell for more than its value on the date of your death, they pay tax only on their profit above the date-of-death stepped-up valuation. Your tax adviser has full details.

DEAR BOB: Several times you've said it's best to get a home seller to finance the purchase. I agree. But how do you find such houses for sale? Tony Y., Washington.

DEAR TONY: It was easy a few months ago to find seller-financed houses because most sellers knew mortgage money wasn't available. Sellers had little alternative but to finance the buyer's purchase. But now that mortgage money is more readily available, some sellers are becoming greedy and demanding all cash.

The best way to find seller-financed houses is to make purchase offers, including seller financing, on houses which interest you. If you make enough offers, one will eventually be accepted. Persistence pays.

DEAR BOB: Please explain the logic of why you say the larger an existing mortgage on a house for sale, the easier it is to sell that house. I always thought it was best to buy out a mortgage as quickly as possible. Kathryn M., Falls Church.

DEAR KATHRYN: The home buyer can either assume most existing mortgages or take title "subject to" the existing mortgage. This avoids the necessity for the buyer to get a new expensive mortgage.

While some mortgage lenders legally can increase the old loan's interest rate when a property is sold, many loans don't allow interest rate increases upon sale (such as FHA and VA home loans) and, in some states, mortgages from banks and nonfederal savings and loan associations.

If a home buyer can take over the existing mortgage, especially in times of tight and expensive mortgage money, this makes the home easy to sell. Any real estate agent will tell you the homes that aren't selling are those with the small or no existing mortgages or those on which the lender can increase the interest rate (thanks to a legally enforceable "due on sale clause").

DEAR BOB: I read in the Real Estate Investing Letter that the IRS reversed itself on Starker "delayed" tax-deferred exchanges. But your recent article said they are still being used. Which is correct? Dan D., Springfield

DEAR DAN: Both are correct. Here's what happened. In June 1979, the IRS issued Private Letter Ruling 7938087 approving an arrangement whereby an investor could qualify for a tax-deferred exchange by selling his property and holding the proceeds in trust until the trustee could acquire other property to complete the trade.

In August 1979, the 9th U.S. Circuit Court of Appeals issued its T.J. Starker decision which approved of the same type of tax-deferred "delayed" exchange. Then in November 1979, the IRS issued Private Letter Ruling 8005049 "reconsidering" and revoking its position in letter 7938087.

To summarize, the T.J. Starker court ruling is still valid. Real estate attorneys are arranging "Starker delayed exchanges" everyday. But the IRS position on such trades isn't clear, so check with your tax adviser or attorney.

P.S. Readers desiring information on the excellent Real Estate Investing Letter can write to HBJ Newsletters, 757 Third Avenue, New York, N.Y. 10017

DEAR BOB: Shame on you for suggesting that "easy way" to evict tenants. While paying a deadbeat tenant $100 or so to move out may be practical and cheaper than a legal eviction, it places a reward on the tenant's wrongful behavior. That's nothing more than tenant blackmail. Roy M., Washington.

DEAR ROY: I agree, but paying a nonpaying tenant to move out usually is cheaper and faster than following the often slow legal eviction procedure.

DEAR BOB: Where might I buy an updated dictionary on real estate terminology? Albert H., Washington.

DEAR ALBERT: There are two good realty dictionaries. One is John W. Reilly's "The Language of Real Estate." It's published by Real Estate Education Co. The other one is the "Illustrated Encyclopedic Dictionary of Real Estate" by Jerome S. Gross, published by Prentice-Hall. Both are available at larger libraries and bookstores.

DEAR BOB: Five years ago, another woman and I bought a condominium for $90,000. We both live in it and are planning on early retirement next year when one of us will be 56 and the other 54. Our condo would probably sell for $160,000. Can only the person over 55 claim a profit tax exemption? What is the best way to take maximum advantage of the tax law? If we wait to sell until we are both over 55, how will that work? Alice M., Alexandria.

DEAR ALICE: Your situation is a classic case of how to get up to $200,000 tax-free profits from the sale of a home. Each qualified unmarried co-owner can claim up to $100,000 in tax-free profits, but a married couple gets only a $100,000 maximum tax-free benefit.

To qualify for the "over rule" $100,000 home sale tax exemption, the owner must be at least 55 on the day of title transfer. The principal residence must be owned and lived in for at least three of the five years before the sale.

Assuming you will split the $70,000 profit equally, is you sell next year only the 56-year-old's $35,000 profit will be tax-free.

But if you wait until both co-owners are over 55, then each co-owner's profit share will be tax-free, up to a $100,000 maximum per owner.

By then the condo will probably have appreciated in value even more, so it may pay to wait. For further details, see your tax adviser.