In a new, more complicated version of one of Washington's most politically potent statistics, the Internal Revenue Service reports that fewer rich people are getting off scot-free on their income taxes.

The service released data this week showing that 57 individuals with adjusted gross income higher than $200,000 owed no federal income taxes on their 1976 tax returns. In 1974, 244 people above the $200,000 bracket escaped taxation, and in 1975, 230 did.

The marked drop results from the Tax Reform Act of 1976, which tightened the rules governing some tax shelters used by the rich to dodge taxation and which increased the "minimum" tax, a surfax designed to assure that all wealthy people pay at least some income tax.

The government has been reporting for years how many wealthy people legally escape income taxes, and the annual statistic has frequently caused a political to-do. In 1969 (when there were 155 wealthy tax dodgers), a crusading Treasury secretary, Joseph Rarr, warned that a "taxpayers" revolt" was in the offing if Congress didn't act to plug loopholes. Barr's campaign led to the imposition of the first "minimum" tax.

In 1976, presidential candidate Jimmy Carter frequently cited the number of wealthy tax avoiders as proof that far-reaching tax revisions were necessary.

Such talk has always rankle Sen. Russell Long (D-La.) who, as chairman of the Senate Finance Committee, is one of the chief architects of the tax provisions that permit high-income individuals to cut their tax burden. Long likes to point out that many of the shelters in the tax code were designed to advance some social or economic goal - and reducing taxes for the rich is a side effect.

In the 1976 tax law, Long added a provision changing the definition of "income" the IRS uses in computing the number of high-income tax avoiders. Long's change was designed to reduce that embarrassing figure.

To offset Long's maneuver, other senators added other amendments calling for definitions of "income" that would increase the figure.

The result is that IRS now computes its annual tax-dodging statistic four different ways.

For comparative reasons, the service continues to compute the statistic based on adjusted gross income, the measure it has used for years. The figures cited at the beginning of this story are based on the traditional standard.

Under the definition of income favored by Long, there were only 33 people with income over $200,000 in 1976 who escaped taxation. Under the figure favored by the opposing group of senators, there were 87 such individuals. Under a fourth measure, which the Treasury Department considers most accurate, there were 67.

One almost needs a master's degree in tax law to understand how the various definitions of income differ. Simply stated, "adjusted gross income" includes most earnings from most sources, but excludes some categories, such as minicipal bond income and some sick pay. Long's definiton subtracted a certain amount from adjusted gross income; the other senators' version added a certain amount.