When President Reagan signed the landmark tax-revision measure into law last fall and proudly proclaimed that its "vanishing loopholes and minimum tax will mean that everybody and every corporation pay their fair share," he must not have had real estate developers in mind.

The rewrite of the tax code was passed partly to ensure that wealthy Americans could no longer shelter large chunks of their income from taxes. But experts believe that real estate developers, who long have used the old code's benefits to virtually wipe out their tax bills, will not be fully covered by the new system for some years.

Magazine owner and real estate magnate Mortimer B. Zuckerman serves as the most recent example of how the tax system for decades legally has permitted such tactics. According to recent court testimony in a Boston lawsuit, Zuckerman has paid no federal income taxes for the last five years -- even though in some of those years he had business and interest income of up to $4 million.

But Zuckerman is far from alone in an industry known for unflagging creativity in minimizing income taxes.

"No self-respecting real-estate operator in the United States pays taxes," said one tax lawyer, who asked that his name not be used because he does so much business with developers.

Some of the tax provisions that Zuckerman and the rest of his industry have used to negate their taxes were cut back in the Tax Reform Act of 1986. Experts say it will be harder for developers to shelter so much income that they pay little or no tax. But some tax breaks were untouched by the law, and many of the new restrictions were phased in, so that their effect will be felt only gradually. Even the stiff new minimum tax contains some exceptions.

"I am not sure you will wind up making real estate {developers} major taxpayers," said former IRS commissioner Jerome Kurtz, now a Washington lawyer in private practice.

According to the Internal Revenue Service, 325 people with incomes greater than $200,000 paid no income tax at all in 1984, the most recent year for which figures are available. A total of 815 taxpayers in that income bracket paid less than 5 percent of their income to the federal government, and another 2,790 paid between 5 and 10 percent in taxes.

And those are extremely conservative figures. An earlier study by the Treasury Department using different assumptions about tax losses taken through partnerships -- a common vehicle in real estate investing -- concluded that nearly 30,000 Americans with incomes over $250,000 paid less than 5 percent of those incomes in federal taxes in 1983. And 3,000 people, 11 percent of those earning more than $1 million, managed to pare their tax bills to nearly zero.

Real estate developers, like many people, are shy about discussing how much in taxes they pay and how they reduce their tax bills. But lawyers and accountants familiar with the industry say the strategy is simple: developers generate more in deductions than they receive in income.

With most Americans, it works the other way around. They subtract their deductions from their income and wind up with a net amount of taxable income. Real estate developers, whose business generates a wealth of opportunities for deductions, wind up with a loss on their tax return's bottom line.

By 1985, for example, Zuckerman had built up cumulative tax losses of $49.7 million, according to abridged copies of his tax returns that are part of the Boston court proceeding. Zuckerman later testified that his tax losses have since ballooned to more than $100 million. The law, new and old, allows those losses to be "carried forward" and applied against income earned for the next 15 years.

"I don't see how this guy is going to pay taxes for a long time, even under the minimum tax," said Robert S. McIntyre, director of Citizens for Tax Justice.

The benefits Zuckerman used to generate those losses were common, garden-variety tax breaks widely used in the real-estate industry. Among them:

Depreciation, the system by which owners of a business asset -- a building, an auto, a typewriter -- account on their tax returns for its loss in value as time passes. Before tax revision, for example, the cost of commercial office buildings could be deducted over a period of 19 years, with the largest writeoff allowed in the early years of the period.

Interest. Just as a homeowner could deduct the interest on his mortgage loan, commercial real estate developers and the investors who team with them could deduct the interest on the debt they incur to buy or build the building. Like home loans, that interest was bunched in the first years of the mortgage term. In later years, a greater proportion of the payment went toward principal and so could not be deducted.

Sales. Developers also could reduce their income when they sold a building, to cut their tax liability. By asking for installment payments, effectively holding the mortgage himself, a builder could receive the sales price over a period of years rather than all at once. And the profits, or gains, on that building were taxed at special, low rates under the old tax code.

The investment tax credit. The old law also subsidized up to 10 percent of the cost of furniture and equipment for the building.

Kurtz described a hypothetical example in which a developer could earn a $40,000 cash profit on a commercial office building -- yet report a $40,000 loss on his income taxes.

It would work this way: The developer would borrow $1 million to build an office building. His payments each year would be about $110,000 -- $10,000 in principal, $100,000 in interest.

Once complete, the building would bring in rent each year of $150,000. The income minus the payments gave the owner a $40,000 cash profit. But that was before the developer sat down and prepared his income taxes.

Under the law in effect until 1986, the developer got a writeoff of $90,000 for accelerated depreciation in the first year the building is occupied. He also could deduct the $100,000 in interest payments, for a total writeoff of $190,000 that offset his $150,000 in rental income. Hence, the $40,000 tax loss.

Developers could employ techniques far more sophisticated than those described in this simple example to cut their tax bills. Zuckerman, for instance, often refinanced his buildings when they were old enough that their depreciation deductions were small, according to Randy Tucker, a lawyer opposing Zuckerman in the Boston case. That generated cash Zuckerman could use to invest in new building,

But the glory days are slowly drawing to a close. Several provisions of the Tax Reform Act of 1986, a law that raised taxes on all American business by $120 billion, will kick in gradually over the next few years to limit the tax-cutting options available to developers.

The most important requires that anyone who engages in so-called "passive" investments, those in which the investor does not play an active managerial role, cannot use losses from those activities to offset other, active income for tax purposes. Zuckerman cannot shelter income that might be produced by his magazines -- the Atlantic Monthly and U.S. News & World Report -- with losses from real estate.

The law also lengthened real-estate depreciation schedules from 19 years to 31.5 years and reduced the amount of the writeoff that can be taken in the early years of the period. It also repealed the investment tax credit.

In theory, that reduces the deduction available to owners of buildings. But the cutback is overwhelmed, developers say, because the passive loss-limitation rules are so strict that even the less-generous depreciation probably cannot be deducted in full.

The minimum tax, a complex mechanism that restricts the extent to which certain deductions can be taken by upper-income taxpayers, also includes several provisions that could hit real estate operators. Depreciation periods are even longer under the minimum tax, for instance, and the installment-sale method of reducing income is restricted.

Under the new tax code, special low rates for capital gains also are ended, so that the top rate for capital gains -- a tax owed on the profit on a building when it is sold -- is 28 percent, the same statutory rate as that applicable to salary income (some well-off taxpayers will face a surcharge resulting in a top rate of 33 percent).

Despite all these restrictions, the losses built up by real estate developers will not necessarily wither away undeducted. Under the new system, as in the old, losses that exceed income in one year can be applied against income in future years, for up to 15 years.

Developers, more than investors, also are more likely to have passive income from rents against which they can apply their losses. The law also phases in the restrictions on passive losses over the next five years, so that such losses are 65 percent deductible this year.