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

The data, in a report that the IRS made public Wednesday night, show 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 $24.4 income of the 400 wealthiest taxpayers in 1992.

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

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

Tax burden

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 same numbers can be read to show that the wealthiest, as a group, bore a disproportionate share of the overall tax burden -- 1.6 percent of all taxes, vs. just 1.1 percent of all income -- evidence that all sides in the tax debate will be able to find ammunition in the new 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 IRS: 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 $26.8 million -- a savings of $12 million, or nearly a third, according to an analysis of the IRS data by the New York Times.

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 McIntyre, said Wednesday that the IRS 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 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 a "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 now relies on the top 1.3 million households for 37.4 percent of individual federal income tax revenues. The poorest half of Americans, who earned less than $27,682 per year in 2000, paid less than 4 percent of income taxes.

All of the IRS data are 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 IRS officials. In all, fewer than 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 IRS advisory panel and is a leading authority on taxation of high income Americans.