DEAR BOB: We gave our buyer a six-month lease with option to buy. That was three months ago. It looks like everything will work out just fine. But can we accept a "stand-by purchase offer" from another buyer in case our first buyer doesn't exercise his purchase option: Mary E., Laurel.

DEAR MARY: Yes. Acceptance of "stand-by offers" is smart. Just be sure you properly word your acceptance of the second buyer's offer so it is conditional upon the first buyer not exercising his purchase option. You may wish to consult your attorney.

DEAR BOB: I offered to buy a house. The offer was good for three days. On the second day I told the realty agent I didn't want the house and was withdrawing my offer. He said I couldn't do that because it was good for three days. On the third day, the seller accepted it. Do we have a valid contract? James M., Annandale.

DEAR JAMES: Probably not. But have your attorney check the offer. The general rule is that an offer can be withdrawn any time before it is accepted unless there is consideration to keep it open.For example, if the seller paid you $100 to hold the offer open for three days, then the seller could accept within the three days even if you tried to revoke the offer.

DEAR BOB: If we move out of our home and rent it to tenants, do we owe any tax? Rolf R., Alexandria.

DEAR ROLF: No. Profit tax is due only when you sell the house.

The Bruss report "How to Sell Your Home With or Without an Agent" is available for 25 cents plus a STAMPED self-addressed envelope sent to Robert J. Bruss, P.O. Box 6710, San Francisco, Calif. 94101.