The Treasury Department uses a computer model to examine the effects of tax cuts on various income groups but does not look in detail fine enough to differentiate among those within the top 1 percent. To determine those differences, The Times relied on a computer model based on the Treasury's. Experts at organizations representing a range of views, including the Heritage Foundation, the Cato Institute and Citizens for Tax Justice, reviewed the projections and said they were reasonable, and the Treasury Department said through a spokesman that the model was reliable.

The analysis also found the following:

Under the Bush tax cuts, the 400 taxpayers with the highest incomes -- a minimum of $87 million in 2000, the last year for which the government will release such data -- now pay income, Medicare and Social Security taxes amounting to virtually the same percentage of their incomes as people making $50,000 to $75,000.

Those earning more than $10 million a year now pay a lesser share of their income in these taxes than those making $100,000 to $200,000.

The alternative minimum tax, created 36 years ago to make sure the very richest paid taxes, takes back a growing share of the tax cuts over time from the majority of families earning $75,000 to $1 million -- thousands and even tens of thousands of dollars annually. Far fewer of the very wealthiest will be affected by this tax.

The analysis examined only income reported on tax returns. The Treasury Department says that the very wealthiest find ways, legal and illegal, to shelter a lot of income from taxes. So the gap between the very richest and everyone else is almost certainly much larger.

The hyper-rich have emerged in the last three decades as the biggest winners in a remarkable transformation of the American economy characterized by, among other things, the creation of a more global marketplace, new technology and investment spurred partly by tax cuts. The stock market soared; so did pay in the highest ranks of business.

One way to understand the growing gap is to compare earnings increases over time by the vast majority of taxpayers -- say, everyone in the lower 90 percent -- with those at the top, say, in the uppermost 0.01 percent (now about 14,000 households, each with $5.5 million or more in income last year).