DEAR BOB: I can buy up to four condominium apartments in a new development. They only require a 10 per cent cash down payment. I would rent them to tenants. Do you think condominiums make good or bad investments? Bernard A., Maryland.

DEAR BERNARD: It's hard to generalize because there are good and bad condominium projects. Condominiums can be great as your personal residence. But I've never heard of anyone getting rich investing in rental condominiums.

To break even, you'll probably need to rent each conodo apartment for at least 1 per cent per month of its purchase price. Most tenants who can pay that stiff rent can also afford to buy. In some areas, renting condominium apartments is very difficult. Check the rental market before you buy.

Upon resale, the percentage appreciation in value for condominiums has usually not been as good as for single-family homes, apartment houses, and commercial properties. So unless you can buy those condos at a bargain price below market value, I would think twice before buying them.

DEAR BOB: Your answer to that poor lady who thought she owned her home with her late husband in joint tenancy with survivorship rights has me worried. She was shocked to find out they owned the houses as tenants in common and the dead husband willed his share to his mother. I don't want to wind up owning my house with my mother-in-law! The deed to our house says we own it in joint tenancy. Is there any way my wife can will her share to here relatives? Harvey T., Virginia.

DEAR HARVEY: When property is owned in joint tenancy, and one joint tenant dies, that share goes to the surviving joint tenant. However, during th joint ternant's lifetime, it is possible in most states for a joint tenant to convery his share to a third party. The party then becomes a tenant in common with the other joint tenant.

Joint tenancy property can't be comveyed by will. One joint tenant can only convey his or her share to a third party while living.

Please don't confuse joint tenancy with tenants by the entireties between husband and wife, which is permitted in a few states. To convey such property during lifetime requires the consent of both spouses.

Joint tenancy is often confused with ownership as tenants in common. Tenants in common can own unequal shares of the property, whereas joint tenants own equal shares. A tenant in common can convey his share to a third party either during his lifetime or by will. Always consult your attorney when taking title to property. Don't let a real estate agent or escrow officier talk you into taking title as joint tenants because "that's what everyone does."

DEAR BOB: We're thinking of renting two or three bedrooms in our large home to college students. If we do so, are there any special tax considerations? Hiriam I., Wheaton.

DEAR HIRIAM: Yes. You'll be able to deduct all applicable expenses for the room rentals. Examples include part of the utilities, maintenance, insurance and all direct costs such as painting the rental rooms. In addition, you can depreciate the rental rooms for wear, tear and obsolescence. All these items are subtractions from the gross rental income.

If you're lucky, you'll have a net cash flow into your pocket but a "tax loss" to subtract from your other ordinary taxable income. The tax loss results from the depreciation, which is a non-cash tax deduction.

DEAR BOB: Recently I inherited a life estate in a 22-unit apartment house. It gives excellent income and is free and clear. On my tax returns for it, can I depreciate this building? Becky A., Bethesda.

DEAR BECKY: Yes. You depreciate the building ove its estimated remaining useful life, just as if you owned the full fee simple. Internal Revenue Code 167(h) says a life tenant can depreciate property.

DEAR BOB: Two months ago the apartment house where I live was sold. I saw the new owner last week and asked him about my security deposit. He said the former owner never transferred my deposit to him.

How can this be? Betty P., Virginia.

DEAR BETTY: When an apartment house is sold, the seller usually transfers to the new owner any tenant security deposits. If that didn't happen when your building was sold, you should immediately contact the former owner before he moves to Afghanistan.Don't hesitate to take him to Small Claims Court, if necessary, to get your security deposit.

DEAR BOB: I'm buying a duplex on a land contract (the seller keeps legal title until I complete my payments to him). Who gets the depreciation deduction until I get the title? Margaret Y., Oxon Hill.

DEAR MARGARET: You do. You have the benefits and burdens of the property so you are the equitable, but not yet the legal, owner. Since the seller is now out of possession, you get the depreciation write-off.

Robert Eruss is an afforney and real estate broker. To get your copy of his report "How the 1976 Tax Reform Law Affects Homeowners and Property Investors," send 10 cents in coin and a STAMPED self-addressed envelope to Robert J. Bruss, P. O Box 6710, San Francisco, Calif. 94101.