DEAR BOB: We are pretty discouraged. We had planned to sell our present home and buy a larger one, but we can't get our present home sold for its full value. Our agent is pretty discouraged too. We had signed a contract, but the buyers couldn't qualify for a new mortgage. As a result, we can't buy the larger home we need. What should we do? Ivan M., Gaithersburg.

DEAR IVAN: Don't give up. But you can forget about your buyer getting a new mortgage in today's market. Today's mortgage crunch is serious, as you discovered. High interesst rates, casued by the Federal Reserve Board's tight money policy, and Jimmy Carter's inflationary federal budget deficits, are the causes. As a result, money is flowing away from traditional mortgage lenders, such as savings and loan associations, into higher-yeilding money market funds.

So you've got to be creative to solve your problems. With the help of your realty agent, you should be able to sell your old home and get enough cash for the down payment on the larger house you need. But if you're expecting an all-cash sale, forget it.

Ideas to consider include:

A lease with option to buy (the buyer's option payment is the equivalent of the traditional down payment.

Taking back a second mortgage and then trading it as part of your down payment on the house you buy.

Having the seller of the house you want to acquire finance its purchase, just as you'll have to help finance your buyer's purchase.

For more creative finance ideas, read Robert B. Allen's outstanding new book, Nothing Down, published this year by Simon and Schuster.

DEAR BOB: What do you think of motels as real estate investments? My wife and I are thinking of buying a small one when I retire next year. Vic D., Rockville.

DEAR VIC: Hotels, motels and boarding houses are businesses first and real estate investments second. Before buying such property, learn the business by getting a job as an assistant manager to see how you like it. If you want to buy yourself a virtually fulltime job, go ahead and buy. But don't say I didn't warn you to get some motel experience first.

DEAR BOB: My husband's business got into trouble with the IRS. They put a lien on his business and our home. We want to sell and move to another area to start over. Is it true that to sell our home we must first pay off the IRS lien? If so, we won't get anything out of the sale. Loretta T., Silver Spring.

DEAR LORETTA: It is true that an IRS tax lien must be paid off when a property is sold so the title can be insured. Your tax advisor or attorney has further information.

DEAR BOB: Do you think, with all the uncertainty in the real estate market, that today is a good time to buy? Davis M., Randallstown.

DEAR DAVIS: Yes. Today is an ideal time to buy since competition from other buyers isn't as keen as it was just a few months ago. You can get some fantastic bargains that weren't available just a few weeks ago. I don't excect property values to decline, but you will see more seller financing available, and that's good for buyers. When mortgage money eases up in cost and supply, the the bargains will disappear. Now is the time to buy and drive a fantastic financing bargain with the seller.

DEAR BOB: We recently bought a condominium apartment where we planned to live. When we inspected it, the tenant living there said she wanted to move out and would vacate within 30 days. She is still there and refuses to leave. She now says she can't find another place she can afford. It turns out she has a lease that has seven months left. Can we evict her, since she promised to move? Kim O., Washington.

DEAR KIM: Property buyers take title subject to the rights of any tenants occupying the property.

If the seller failed to warn you of the lease, he may be liable to you for the resulting monetary damages. Even though the tenant verbally told you she would be moving out, a judge would probably not evict her since she has a written lease. Your attorney can further clarify the situation.

DEAR BOB: In 1979 I made the mortgage payments for my father on his house. He is disabled. When I went to have my tax returns prepared, the IRS agent said I can't deduct the interest since I wasn't obligated on the loan. I made the payments. Can't I deduct them as an itemized interest? Hattie Y., Springfield.

DEAR HATTIE: No. You must be legally obligated to pay the loan if you are to be entitled to deduct the interest. If you were a co-signer or a guarantor, however, then you would be entitled to the interest deduction. if the primary obligator, your father, is unable to pay. Perhaps you should have your name added to the loan so you can deduct the interest you pay in 1980.