New tax trouble is brewing on Capitol Hill that could seriously affect real estate investors and first-time home buyers. No Senate or House leaders have announced their legislative plans yet, but the word is seeping out of key congressional committees: Real estate is high on the tax increase list for 1983.

Billions of dollars of new federal revenues can be generated by taking what one congressional expert calls "a few whacks out of the plentiful hide of the real estate sacred cow."

Two important, current tax incentives for housing -- one setting guidelines for depreciation deductions and the other allowing use of tax-exempt bond financing for moderate-income home buyers -- are likely to go on the chopping block early in the new Congress, according to a tax committee staff member.

Here's how the tax changes could work, and how they might affect you:

The first chop would hit anyone investing in income-producing real estate, including small-scale rental houses or duplexes, condominiums that are rented rather than sold, apartment buildings and commercial properties, such as office buildings.

Congress would take back part of the favorable depreciation (or "cost recovery") incentives provided in the 1981 Economic Recovery Tax Act. Rather than being able to write off income-producing property over 15 years, as now permitted by law, investors would be rolled back to a 20-year standard depreciation term.

What may seem like an innocuous reform at first blush would have two major impacts. It would put many real estate investors in a worse position than they had been under the cumbersome, pre-1981 rules. And it would put a huge chunk of cash into the federal revenue pot.

Congress' Joint Committee on Taxation estimates that over $13 billion could be raised during the next five years simply by extending the depreciation period. The longer the write-off period, in other words, the less that can be deducted year by year during the deficit-ridden 1980s. The less that's deducted, the more that goes to the Treasury.

"Thirteen billion is a very tempting number," said one congressional committee staff expert. "It just jumps out at anyone up here who's desperately looking for places to cut the deficit. Thirteen billion solves a lot of problems."

But rolling back the standard depreciation schedule for real estate may also create sizable problems for housing.

New construction of moderate-income rental buildings, for example, would be significantly less attractive to investors if the tax write-offs are slashed. A typical investor in a small, modest-cost, new rental apartment project could lose close to $2,000 in depreciation deductions per unit during the first 24 months of the amended law alone, according to one estimate. A building with 100 units would produce $200,000 less in depreciation deductions.

Since investors bank heavily on getting immediate tax benefits -- rather than net income -- from rental apartments, any substantial cut in those benefits would tend to discourage new rental construction projects.

With rental housing already in short supply in most cities -- and relatively few new nonfederally subsidized apartment projects under construction -- Congress' revenue-raising move could backfire. It might not raise the $13 billion in new tax collections at all; it might depress construction activity further and create far fewer new buildings to tax than the experts thought.

The second large real estate item on Congress' "chop" list involves single-family homes for first-time buyers.

One of three first-time home purchasers in the United States this year has received a mortgage with a slightly below-market rate. Those mortgages -- $7.5 billion worth on 150,000 homes -- have been financed by state, city and county agencies who issue tax-exempt housing bonds. Nearly every state has a "housing-finance agency" (HFA) to issue such bonds, as do many municipalities.

These are not public housing bonds or low-income projects. They are moderate-cost new and resale condominiums, cooperatives and detached homes, with average loan rates of 11 to 14 percent.

Legal authority to issue such bonds, however, will expire in 1983. The bonds are currently exempt from federal taxes and have long been a target of tax-writing committees on Capitol Hill.

Unless Congress acts to preserve the bonds' tax-exempt status--and the early rumblings are that it won't -- a key source of mortgage money for first-time home buyers will dry up next year.