DEAR BOB: If I sell my house and buy a duplex where I live in one half, can I defer my profit tax? Lester 8., Washington.

DEAR LESTER: Yes, if the value of your personal residence half of the duplex exceeds the sales price of your principal residence and if the duplex is purchased with 18 months before or after the sale. See your tax advisor for full details of the "residence replacement rule."

DEAR BOB: Recently I learned about "reverse mortgages" in your column. That would be perfect for my mother, who lives in Tampa and badly needs extra money to live on. She owns her home free and clear. I contacted several banks and savings associations in the Tampa area but they have never heard of reverse mortgages. Where can I get one for my mother? Richard F., Gaithersburg.

DEAR RICHARD: Each week I receive many letters asking where to get a reverse mortgage, which lends a homeowner a fixed amount of his or her equity each month. Unfortunately, these new experimental mortgages are only available in the Cleveland area (from Braodview Savings and Loan Association). As far as I know, they are not yet available elsewhere.

For more details on reverse mortgages, write to the U.S. League of Savings Associations, 111 East Wacker Dr., Chicago, 60601. I'll let you know when they become more widely available.

DEAR BOB: You said it is possible to get 90 and 95 percent "PMI" home loans. FHA and VA home loans are hard to get where I want to live because so many sellers refuse to pay the required loan fees. Where can I get one of those "PMI" mortgages? James L., Fairfax.

DEAR JAMES: PMI (private mortgage insurance) mortgages are available from most banks and savings associations. Over 22,000 lenders now make these loans for 90 to 95 percent of the market value of homes. Most resale homes qualify for the 90 percent loans and new homes can qualify for the 95 percent mortgages. So your down payment is only 5 or 10 percent of the purchase price.

These PMI laons, while costing about 1/4 percent more than conventional home mortgages, offer fast, one-day approval in most cases. The seller doesn't pay any of the cost. In many communities, more PMI loans are now made than FHA and VA mortgages combined. Ask a real estate agent for complete details.

DEAR BOB: We bought a condeminium apartment that we plan to occupy in about five years. In the meantime, we rent it to a tenant. Our tax man says we can depreciate 95 percent of our purchase price. This sounds very high to me. Is it true or is our tax man wrong? Hanley R., Bethesda.

DEAR HANELY: Your tax man is probably correct in his apportionment of the land (5 percent) to building (95 percent) ratio for depreciation purposes. The non-depreciable land value is low because you own only a tiny share of the land as a tenant in common with the other condo unit owners.

DEAR BOB: My wife and I are in our early 20s and want to buy our first house. We both have good jobs and can afford the monthly payments on a home priced up to about $60,000. Our problem is getting together the huge cash down payment before prices go up more. Are there any ways to buy a house without a big 15 to 20 percent down payment? Dana. B., Rockville.

DEAR DANA: Yes, there are several excellent methods. Hundreds of people like you buy their first homes every day. If they can do it, you can too. Here are some finance ideas to consider.

(1) Lease a house with option to buy it in six to 12 months. Many local home resale markets are slow now. Sellers are anxious. Try offering to lease a house with an option to buy later. Ask for full or partial credit for rent paid toward the purchase price (this is your down payment). If possible, get the seller to agree to carry the first or second mortgage too. This won't work with every seller, but keep trying until it works for you.

(2) Low-down payment FHA, VA and PMI mortgages. FHA mortgages are available up to $60,000 with only about 4 percent average down payments. VA home loans up to $70,000 require no down payment for qualified veterans. PMI (private morgage insurance) mortgages finance 90 percent of the home's purchase price through more than 22,000 banks and savings associations.

Work with a good real estate agent to find and finance the right house or condominium for you.

DEAR BOB: Is there any guideline about the right time to refinance income property? Beck M., Vienna.

DEAR BECKY: Refinance when your cash flow from the income property becomes taxable. This happens when the annual mortgage equity buildup exceeds the building's depreciation tax deduction.

The benefits to you of owning income property should include (1) taxfree cash flow, (2) tax loss to shelter some of your other earnings, such as job salary, and (3) probable resale appreciation in market value.

DEAR BOB: Mortgage lenders in our area are now demanding big cash down payments on home purchases before they will make a new mortgage loan. We don't have that much cash. Is there any way to buy a home without paying 25 or 30 percent of the purchase price for the down payment? Garcia R., Washington.

DEAR GARCIA: Yes. There are many ways to use creative real estate financing to buy a home. But don't forget that the best finance source of all is the home's seller. Many sellers, especially retired people, will either finance the entire first mortgage or at least a second mortgage to fill any finance gap between your down payment and a new first mortgage.

For example, I recently bought a rental house on which the seller agreed to take back a first mortgage at 9 percent interest, which is below current conventional mortgage rates in my area. But when I made my purchase offer, the agent didn't think the seller would carry the mortgage, as she had never indicated she would. Not every seller will finance a home's sale, but it won't hurt to provide for seller financing in your purchase offer.

For more finance ideas, read my report "How to Use Creative Realty Finance Ideas for Profit," available for 25 cents plus a self-addressed stamped envelope, from Robert J. Bruss, Box 6710, San Francisco 94101.

DEAR BOB: We bought a new home and want to sell our old house and use the cash to buy investment property. How can we best minimize that tax on our $35,000 profit? Sylvia M., Warrenton.

DEAR SYLVIA: If you rent your former residence to tenants, thus converting it to investment property, then you can make a tax-deferred trade of it for investment property. See your tax adviser for full details.