If you've been wondering whether to get involved in small-scale real estate investment for the first time -- or to increase your property investments further -- take a hard, close look at the new tax bill signed by President Reagan.

In general, the law is a big plus for real estate and offers savvy investors opportunities they never had before.

But there are a few soft spots and pitfalls tucked away in the law that you ought to focus on before plunging into new acquisitions or sales.

Here's a quick, tactical overview:

On the plus side, you'll love the new "audit-proof" depreciation schedules. The Internal Revenue Service no longer will be able to hound owners of rental homes, duplexes and other small-scale investment real estate about the "useful lives" of their properties.

Beginning with real estate acquired anywhere in the United States as of Jan. 1 of this year, all residential and commercial property will be defined as having a standard 15-year economic life. The IRS won't be allowed to challenge that fact.

The significance of this won't be lost on anyone who's ever invested in real estate. Depreciation deductions -- the write-offs permitted under the tax code to compensate for the gradual deterioration of a property -- have been based on 30- to 40-year "useful lives" since the 1960s.

A rental duplex or condominium that can be depreciated over just 15 years is a substantially better tax shelter to the typical investor than the same building depreciated over 35 years. It can be written off, year by year, more than twice as fast. A $100,000 investment depreciated over 40 years "straight line," for instance, provides just $2,500 a year in deductions. The same investment depreciated on a 15-year scheduled provides $6,700 in annual write-offs.

The new law sweetens the tax-shelter appeal of real estate even further. Most investors will use what is known as accelerated, 175 percent "declining-balance" depreciation to inflate deductions in the early years after they buy a piece of real estate.

A $100,000 property depreciated in this manner under the new law would produce nearly $12,000 in first-year deductions.

Another important area of investment opportunity expanded by the 1981 tax code revisions is in the field of property rehabilitation.

The new law provides generous tax credits -- which have more bang for the buck than regular deductions -- to anyone who rehabilitates older, commercial structures or historic properties.

In addition to 15-year depreciation, the law gives the buyer of a residential or commercial property located in an historic district -- or a property that is a federally certified historic structure in its own right -- a 25 percent credit on rehabilitation expenditures.

For investors who buy and rehabilitate small stores, office buildings or other commercial buildings that are 30 years of age or older, the tax credit ranges in size from 15 to 20 percent.

In the words of one nationally known real estate investor and rehabilitation expert, Craig Hall of Southfield, Mich., the new law "is going to be a gold mine for small groups of investors who know how to spot older or historic buildings with "turnaround' potential. The government is now saying to investors, in effect, 'Look -- we'l make you rich if you'll rehabilitate buildings rather than knock them down.'"

Since qualifying 30-year-old and older buildings are plentiful across the country -- in small towns as well as big cities -- Hall thinks this will be one of the most significant provisions of the new law.

On the minus side of the tax-code changes, be aware of the following:

The IRS will be watching real estate investors closely for any sign that they are selling one another properties simply to qualify for the liberal new depreciation deductions. Houses, rental condos, apartment buildings and other properties acquired prior to 1981 are stuck with the "old," less-generous deduction schedules. If you buy in 1981 (and hereafter), you should qualify for the new, generous write-offs. However, if two friends or business associates swap their buildings this year simply to cash in on the 15-year write-offs, the IRS promises to get very nasty.

The historic and commercial-property rehabilitation regulations contain some technical snares for the unwary. These relate to the extent of the rehabilitation carried out and the maximum amount of depreciation taxpayers can claim. Don't attempt to jump into this sort of investment without careful, professional guidance by a tax attorney or accountant.