DEAR BOB: It's pretty discouraging for young couples like us when we realize that we may never be able to afford a home of our own. My father told us, when we got married two years ago, to wait to buy a home until mortgage interest rates came down. So we saved our money for a down payment. We've got about $4,900 now. But I see mortgage interest rates are still sky-high and you recently said you don't expect them to come down soon. What should we do? Shirley M., Bethesda.

DEAR SHIRLEY: Buy a home today before prices and mortgage interest rates go higher. With the government creating printing press money, which fuels inflation, don't expect mortgage prices to decline any time soon, if every.

Similarly, mortgage interest rates aren't likely to decline, partly because of continued expectations of high double-digit inflation. In addition, savings associations will have to pay higher interest rates to savers in 1980, so they must write mortgages at high rates.

You should be aware that mortgages are one of today's true bargains for two reasons. One is that after the income tax deduction for interest paid, the true rate is lower than you think. Suppose you get a mortgage today at 11 percent and that you are in a 30 percent income tax bracket. Thirty percent of 11 percent is 3.3 percent; 11 percent minus 3.3 percent is 7.7 percent, which is your true, after-tax bargain rate. Where else can you borrow so cheaply?

The other is that the house or condominium you buy, if it is well-located, should go up in value at least as fast as the inflation rate. The net result is that you make a profit while you enjoy a home of your own.

DEAR BOB: In July I sold my four-plex -- and made a net profit of $97,000. If I reinvest that money in a larger apartment house, is it true that I can avoid paying tax on my profit? Stella M., Washington.

DEAR STELLA: No. There is no way to sell property, other than your principal residence, and defer the profit tax by buying a more expensive replacement. Many people share your thinking. I guess ignorance loves company. Next time, consult your tax advisor before selling.

DEAR BOB: In two weeks we are to close on our new home. What is the best way to be sure it's in good shape and that the seller left the appliances and carpets he promised? Bruce Q., Wheaton.

DEAR BRUCE: The day before the closing settlement, ask the agent to reinspect the house with you. Before the closing you have maximum leverage over the seller if anything is wrong. But after the sale closes and the seller has your money, he could care less if you're not satisifed.

DEAR BOB: I am 49 and my wife is 47. Due to heavy medical bills, we must sell our home. I was disabled in an auto accident.As our sale profit will be about $68,000, is it true that disabled people qualify for that new $100,000 home sale tax exception? Ken M., Alexandria.

DEAR KEN: No. When the law was originally proposed, it contained a provision making disabled persons eligible for the "over 55 rule" $100,000 home sale tax exemption. But the final version of the law deleted this clause. The law only applies to home sellers who are age 55 or older who have owned and lived in their principal residence at least three of the five years before sale. Ask your tax advisor for further details.

The new Bruss report, "How to Buy a Home for the Lowest Price and on the Best Terms," is available for 25 cents plus a self-addressed, stamped envelope sent to Robert J. Bruss, P.O. 6710, San Francisco, Calif. 94101.