Texas Gov. George W. Bush today made his case for across-the-board tax cuts, repeatedly evoking the image of a single mother, waitressing for a living, to typify those who would benefit most from his plan to reduce taxes by more than a trillion dollars over a decade.

But the Republican presidential front-runner drew immediate criticism from the political left, which accused him of promoting an excessively expensive plan that would help middle- and upper-income families far more than the working poor. And his conservative rivals charged that his plan would merely further complicate the tax code instead of providing needed reform.

In outlining his plan, Bush said he wants to reduce what he termed record-high tax levels and to help Americans move up the income ladder. He proposed reducing tax rates for all income brackets, phasing out the estate tax, doubling the $500 child tax credit, reducing the marriage tax penalty and expanding the charitable deduction benefit.

His plan would also permanently extend a research and experimentation tax credit that is highly popular with high-tech industries, but Bush did not propose a further reduction in the capital gains tax, a top priority of many conservatives.

The Bush campaign on Monday leaked many of the plan's details, which were reported today by The Washington Post and several other newspapers. Even before Bush delivered his speech before several hundred members of the Des Moines Chamber of Commerce, many of his Republican and Democratic rivals had already condemned his tax proposals as too weak or misguided.

"He leaves the IRS unchanged, the complexity issues unchanged, and he phases it in over five or eight years," Republican presidential candidate Steve Forbes, a proponent of a flat tax, said in an interview. "Why does he pass up the opportunity to make major change?"

Sen. John McCain (R-Ariz.) complained that Bush's plan is too expensive and would squander budget surpluses that could be put to better use. "We ought to protect the Social Security fund, and we ought to look at it very carefully," McCain said. "In my tax proposals, we pay for it. We pay for it by cutting appropriations and eliminating special interest loopholes and benefits."

Campaigning in Iowa, Vice President Gore sought to lump together Bush's costly tax-cut plan with the health care reform initiatives of his Democratic opponent, Bill Bradley. "It is astonishing to me that both Governor Bush and Senator Bradley just can't keep themselves from using up the entire 10-year surplus," Gore said. "It's like a big cookie jar and they just can't help from using it all up and emptying it all out."

Gore was so eager to attack Bush's plan that he interrupted an open meeting in Sioux City to announce that he would hold a second news briefing to further denounce the plan.

During his speech and in a meeting later with reporters, Bush repeatedly stressed that his plan benefits lower-income families, as a way of underscoring his "compassionate conservative" campaign message. He maintained that half of the overall cost of his tax cuts would be accounted for by changes designed to help low-income families enter the middle class.

In using the example of a single waitress earning $22,000 a year, Bush said that as the woman begins to earn more money, "the marginal rate--the extra taxes on every dollar earned--is higher than [for] the stock broker making $220,000."

"And that's not right," he said, adding that his program is designed "to make sure there is mobility to get into the middle class." As part of that effort, he said, one in every five families with children would no longer pay any income taxes.

But officials of several liberal budget and tax policy groups complained that the majority of working-poor families that pay little if any income taxes would get no help from Bush's program, while the bulk of the benefits would go to wealthier Americans.

Two-thirds of the benefits would go to the wealthiest 10 percent of Americans, who would receive tax cuts averaging $8,362 a year, according to an analysis by Citizens for Tax Justice. By comparison, taxpayers in the lowest 60 percent of the income scale would get only 11 percent of Bush's tax cuts, with an average cut of only $249, the study said.

Robert S. McIntyre, director of the tax group, said that in terms of who would benefit most, the Bush plan is remarkably similar to the one passed by congressional Republicans last summer and vetoed by President Clinton. "The biggest difference is that the Bush plan is even more irresponsible, since it would cost twice as much," McIntyre said.

The plan, meanwhile, received mixed reviews from conservative groups. Grover Norquist of Americans for Tax Reform praised the plan for abolishing the estate tax, lowering income tax rates across the board and moving toward a "flatter, fairer" tax system.

Bill Beach, an economist with the conservative Heritage Foundation, described the plan as a "relatively aggressive tax package compared to what we've seen coming out of Washington during the last few years," but he questioned whether Bush was moving toward the fundamental tax reform that is needed. "This proposal is full of targeted tax cuts," he said, adding that once "you create a tax provision for a group, it's very hard for that group to give it up."

Neal reported from Des Moines, Pianin from Washington. The details of Bush's tax proposal are available on the Web at www.washingtonpost.com.