he 400 wealthiest taxpayers accounted for more than 1 percent of all the income in the United States in the year 2000, more than double their share just eight years earlier, according to new data from the Internal Revenue Service. But their tax burden plummeted over the period.

The data, in a report that the I.R.S. released last night, shows that the average income of the 400 wealthiest taxpayers was almost $174 million in 2000. That was nearly quadruple the $46.8 million average in 1992. The minimum income to qualify for the list was $86.8 million in 2000, more than triple the minimum income of $24.4 million of the 400 wealthiest taxpayers in 1992.

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While the sharp growth in incomes over that period coincided with the stock market bubble, other factors appear to account for much of the increase. A cut in capital gains tax rates in 1997 to 20 percent from 28 percent encouraged long-term holders of assets, like privately owned businesses, to sell them, and big increases in executive compensation thrust corporate chiefs into the ranks of the nation's aristocracy.

This year's tax cut reduced the capital gains rate further, to 15 percent.

The data from 2000 is the latest available from the I.R.S., but various government reports indicate that salaries, dividends and other forms of income have continued to rise since then, even as the stock market has fallen.

The top 400 reported 1.1 percent of all income earned in 2000, up from 0.5 percent in 1992. Their taxes grew at a much slower rate, from 1 percent of all taxes in 1992 to 1.6 percent in 2000, when their tax bills averaged $38.6 million each.

Those numbers can be read to show that the wealthiest, as a group, carried a disproportionate share of the overall tax burden — 1.6 percent of all taxes, versus just 1.1 percent of all income — evidence that all sides in the tax debate will be able to find ammunition in the data.

In 2000, the top 400 on average paid 22.3 percent of their income in federal income tax, down from 26.4 percent in 1992 and a peak of 29.9 percent in 1995. Two factors explain most of this decline, according to the I.R.S.: reduced tax rates on long-term capital gains and bigger gifts to charity.

Had President Bush's latest tax cuts been in effect in 2000, the average tax bill for the top 400 would have been about $30.4 million — a savings of $8.3 million, or more than a fifth, according to an analysis of the I.R.S. data by The New York Times. That would have resulted in an average tax rate of 17.5 percent.

The rate actually paid by the top 400 in 2000 was about the same as that paid by a single person making $123,000 or a married couple with two children earning $226,000, according to Citizens for Tax Justice, a labor-backed group whose calculations are respected by a broad spectrum of tax experts.

The group favors higher taxes on the wealthy, and its director, Robert S. McIntyre, said yesterday that the I.R.S. data bolsters that viewpoint. "Regardless of which party these 400 are in, these are the guys Bush wants to help, even though they have so much money they don't know what to do with it," he said. "How Bush feels about the half of the population that doesn't have much money is he got them a tax cut worth an average of $19 each."

William W. Beach, a tax expert at the Heritage Foundation, a conservative organization that favors lowering taxes for all Americans, said that the top 400 taxpayers made "the significant contribution" to government revenue — about one in every $64 of individual income tax paid. Cutting taxes, he said, will prompt the wealthy to invest more in the economy's growth.

Detailed information about high-income Americans has become increasingly important in setting tax policy, because the government relies on the top 1.3 million households for 37.4 percent of individual federal income tax revenue. The half of Americans who earned less than $27,682 in 2000, paid less than 4 percent of income taxes.

All of the I.R.S. data is based on adjusted gross income, the figure reported on the last line on the front page of individual income tax returns. Interest earned on municipal bonds, which are exempt from tax, is not included.

Over the nine years of tax returns that were examined for the new report, only a handful of taxpayers showed up in the top 400 every year, according to I.R.S. officials. In all, about 2,200 taxpayers made the cut even once. There were a few incomes of more than $1 billion a year in the group, but none as high as $10 billion.

The names of the wealthiest taxpayers are not disclosed in the report, which was prepared at the urging of Joel Slemrod, a University of Michigan business school professor who serves on an I.R.S. advisory panel and is a leading authority on taxation of high-income Americans.

The figures do not include the incomes of the many wealthy Americans who use shelters to reduce their reported incomes below the level of the top 400.

In 1999 and 2000, for example, William T. Esrey — then the chief executive of Sprint, the telecommunications company — earned more than $150 million in stock option profits, lofting him onto many lists of the best-paid corporate managers.

That income might have put Mr. Esrey in the I.R.S.'s top 400 taxpayers. But, as later came to light, Mr. Esrey bought a tax shelter from Ernst & Young, the accounting firm, designed to let him delay reporting the profits for tax purposes until the year 2030. Sprint's board forced Mr. Esrey to resign in March after he acknowledged that the shelter was the subject of an I.R.S. audit.

Over the nine years reviewed in the new report, the incomes of the top 400 taxpayers increased at 15 times the rate of the bottom 90 percent of Americans; their average income rose 17 percent, to $27,000, from 1992 to 2000.

Long-term capital gains accounted for 64 percent of the income of the top 400 in 2000, nearly double the level in 1992. Wages contributed 16.7 percent to the incomes of the top 400 in 2000, down from 26.2 percent in 1992, and dividends made up 2.8 percent.

A second report that the I.R.S. will make public today shows that the number of Americans with high incomes who pay no taxes anywhere in the world has reached a record. In 2000, there were 2,022 Americans with incomes of more than $200,000 who paid no income tax anywhere in the world, up from just 37 in 1977, when the report was first issued.