DEAR BOB: Our home is listed for sale. The agent called on a Sunday morning to say she had a purchase offer for us.We were on our way to church so we made an appointment for 2 p.m. the same day. Just before 2 p.m. the agent phoned to say the buyer had withdrawn his purchase offer. Can this be done? Mrs. J. S., Alexandria.

DEAR MRS. J. S.: Yes. An offer can be withdrawn any time before its acceptance. For this reason, real estate agents are extremely anxious to get a purchase offer presented to the seller before the buyer catches "buyer's remorse." This is a disease that causes buyers to withdraw their purchase offer before the seller accepts. If it strikes after the offer is accepted, there is little the buyer can do. Fortunately, these misgivings usually go away in a few days when the buyer realizes the wisdom of his purchase.

DEAR BOB: I sure wish our newspaper had been running your articles when we first started investing in real estate back in 1968. We could have used your advice, but somehow we got over the hurdles. As a result we now own 12 properties, all bought as the result of a $6,000 initial investment. Today, due to inflation, I think it would take about $10,000 to get started, however. Perhaps our experience can help others. Our goal was to buy one investment property a year. By refinancing our existing holdings, we've managed to do that.

In 1978 we sold one small duplex apartment to give us cash for our son's college tuition. Next year we'll sell another building to pay for more tuition. In four years, we'll sell another building on an installment sale to provide for our retirement income. Then we'll sell off buildings as we need the cash. That's not too bad for a taxi driver with a ninth-grade education, is it? Claude R., Washington.

DEAR CLAUDE: Thank you for your marvelous letter. It shows how wise property investment can provide long term security.

DEAR BOB: We have twice used that "residence replacement rule" you often mention to defer the profit tax on homes we've sold. What happens to that deferred profit tax when my husband or I die? Mo M., Springfield.

DEAR MO: Nothing. The deferred profit tax is forgiven when the owner dies. Of course, the decedent's estate may be taxed on the market value of the property involved, but the deferred profit tax is forgiven at death under present law. It's a rather extreme and irrevocable way to avoid tax, but it's the law. Ask your advisor for full details.

DEAR BOB: If you were buying a home in today's market, how would you finance your purchase? We are a young couple, ages 22 and 24, with only $4,000 in savings for a down payment. In our area, that's hardly enough for a shack. Giner and Fred H., Rockville.

DEAR GINGER AND FRED: Don't get discouraged. More than ever before, persistence pays off today when looking for a home to buy.

When you find a home you like, make an offer. Offer your $4,000 down payment and provide for the seller to finance the rest of the sale price on either a second mortgage or a wrap around mortgage. Not all sellers will accept, but if you make enough offers you'll find one who will.

Another finance technique is to lease a house for 12 months with an option to buy. All or part of your rent will be credited toward the purchase price if the owner agrees. The big lease-option advantages include a small cash requirement, locking in the purchase price of the house a year from now (when prices will be higher today), and avoiding today's high cost mortgage market. Your realty agent will have other finance ideas.

DEAR BOB: We have a least $60,000 equity in our home. Is now a good time to refinance the mortgate to make out some of this equity? Ford E., Annapolis.

DEAR FORD: No. Mortgage money is extremely tight and expensive now. Only if you have a use that would yield more than the high cost of interest would it be wise to refinance now. The time to refinance is when mortgage money is easy to find and lenders are falling over themselves to lend money. Now is not that time.

DEAR BOB: I recall your answering this question before but I can't remember the answer. If we sell our home, and buy a more expensive one, do we have to reinvest all the sale cash into the replacement to qualify for the profit tax deferral? Angela M., Fairfax.

Dear ANGELA: No. To qualify for the "residence replacement rule," you must buy a more expensive replacement principal residence within 18 months before or after selling your present principal residence. If you build a new home, you can take up to 24 months after the sale to move in.

The law says nothing about reinvesting even $1 from the sale preceeds into the replacement. If you wish, you can get a 100 percent VA mortgage on your replacement home and spend the sale proceeds from your old home as you wish without paying tax on your profit. Your tax advisor has details.

DEAR BOB: We own some rural land that we would like to have appraised. Several real estate brokers have given us widely varying estimates of what we can get for it. I think that before we put the land up for sale we should have a professional appraisal done. What is the best way to find a competent appraiser? Lavonia M., Annandale.

DEAR LAVONIA: Hire a professional appraiser who is a member of one of the major appraisal societies. You can find these people listed in most Yellow Pages under Appraisers or Real Estate Appraisers. Be sure the appraiser you hire is experienced in appraising rural land.