DEAR BOB: A long time ago you told us where realtors buy those little books with the various monthly mortgage payment tables at different rates of interest. Please give the details again.

DEAR GWEN: The superb 1977 Realty Bluebook is pocket size with 400 pages of loan payment tables, loan balance tables, mortgage discount forms and phrases. You can get one for $12.72 from Professional Publishing Corp., 122 Paul Avenue, San Rafael, Calif. 94903. Ask for their free samples of real estate forms, which are also outstanding.

DEAR BOB: Does the IRS allow tax deduction of mortgage interest, plus the property tax and depreciation, on a house rented for less than the total of these deductions? In other words, can I use a net loss to reduce my other taxable income?

DEAR ATHOS: Yes. It is very common for income property to produce a "tax loss" after deducting the operating expenses, plus depreciation, from the rental income. In fact, investors buy income property to use the tax loss to offset some of their other taxable income. However, if your rental is a vacation home, which you use partly for personal use, then tax loss deductions exceeding rental income are not allowed if personal use exceeds 14 days per year or 10 per cent of the rental days.

DEAR BOB: We bought our house directly from the seller. No agent. Somehow the property tax was overlooked.We had to pay the entire year's property tax. But our CPA says we can only deduct our share for the time we owned the house. Is he correct?

DEAR EVAN: Yes. Property buyers and sellers must apportion the property tax according to how many days in the tax year they owned the property. If this isn't done, you can deduct on your income tax return only your share even though you paid the entire property tas bill to prevent a tax lien from being filed on your house.

DEAR BOB: Recently I attended a tax planning class. The instructor talked about composite and component depreciation on income properties. What is the difference and which is better?

DEAR HIRAM: The composite depreciation method (the most widely )used) is an average rate of depreciation applied to an entire building, including its roof, shell, heating, wiring, and plumbing. Component, or separate, depreciation means each element in the building it depreciated separately. The component method usually gives bigger depreciation deductions in the early ownership years than the composite method. Faster write-off too.

For example, suppose you buy a brand new apartment house. The IRS says you should use a 40 year composite useful life for it. But if you select the component method, you might depreciate the roof in 15 years, the plumbing in 20 years, the building shell in 50 years, etc. for bigger total deductions in the early years. You can use straight line or accelerated rates. Both methods can now be used on resale buildings as well as new construction.