WASHINGTON – Some of President Bush’s most loyal supporters were furious at him yesterday after he left the door open to a huge tax increase of the very sort that he campaigned against in the election.

Mr. Bush said he is open to making more wages subject to the Social Security payroll tax. The 12.4% tax currently applies to salaries up to $90,000. “The only thing I’m not open-minded about is raising the payroll tax rate. And all other issues are on the table,” the president said this week.

The increase would inflate tax bills of people who earn more than that amount, and it would be particularly noticeable to self-employed people who pay both an employee and employer share of the tax.

The increase would be “a declaration of war on the Republican base – which is made up of people who would get whacked by this tax,” said the president of Americans for Tax Relief, Grover Norquist.

“I am not happy,” said Mallory Factor, the co-founder of the Monday Meeting in New York, a large conservative discussion and fund-raising group. Most members of his group are enthusiastic about the president’s proposal to divert Social Security contributions into private accounts invested in the stock market, he said, but they would balk at a tax increase.

“The president will be perfectly fine with his loyal supporters if he abandons his idea,” said Pat Toomey, the president of the Club for Growth, a powerful fund-raising group for Republicans. “If he doesn’t, then I think there is a problem.”

Mr. Toomey said he has already called the White House and is awaiting clarification of the president’s remarks.

The chief economist at the Chicago investment bank Griffin, Kubik, Stephens & Thompson, Brian Wesbury, who has advocated in favor of the planned accounts, said he was “shocked” and “disappointed” by the president’s comments.

The idea would be so disastrous economically and politically that it would be better that the president not do personal accounts at all, Mr. Wesbury said.

“This would be the equivalent of his father breaking the ‘Read my lips’ tax pledge,” he said. Mr. Norquist went farther, saying the tax increase would be “even worse, because it would show we didn’t learn last time.”

Removing the cap completely would push marginal tax rates to their highest levels since the Reagan tax cuts of the 1980s, calculated Mr. Wesbury, a former chief economist for the Joint Economic Committee of Congress. The top marginal tax rate would reach 53%,he said.

The tax increase would “undermine the very program he is trying to create” by hurting equity markets and reducing returns in the proposed private accounts, Mr. Wesbury said.

“Getting accounts in exchange for raising taxes is an exchange that will be a net loss to society and to the Republican Party,” he said.

Congressional Republicans privately doubted that the idea would get anywhere on Capitol Hill.

“While we applaud the president’s effort to encourage everybody to bring all ideas to the table, the idea of raising the cap is a nonstarter for us,” said a Republican leadership aide in the House, who declined to be named.

Another senior GOP Senate aide said, “Anyone thinking Republican majorities in Congress will go for a tax hike is not living in the real world. Taxes have been raised on Social Security over 20 times and failed to fix the problem. They don’t work and they kill jobs, period.”

The comments also sparked speculation that the president was running out of options for wooing critical Democrats and preventing a filibuster on the proposal in the Senate.

But some Republicans doubted it would sway a single Democrat.

“If you negotiate with the Democrats, you have to have everything on the table,” Mr. Norquist said. But since the proposal is unlikely to get passed in the House and Senate, he said, “putting it on the table isn’t credible.”

Mr. Norquist said the president was making his supporters uneasy.

“What if your husband said to you, ‘I’m not in favor of adultery, but I think it should be an option on the table, but I wouldn’t do it, but I think it should be on the table.’ It just makes people nervous,” he said.

David Keating, the executive director of the Club for Growth, said, “There is a real danger he could lose a lot of support among Republicans for the accounts if he is open to the idea of raising taxes to make it happen.”

However, Mr. Factor did not expect the club’s members to withdraw their support for the president or the GOP on account of it. “I really don’t, I’m sorry to say, because the alternative is much worse,” he said, referring to the Democratic Party.

At a press conference yesterday, Mr. Bush was asked to explain why increasing the cap on payroll taxes does not amount to a tax increase. The president did not answer the question directly and instead emphasized that he is “willing to discuss” ideas from members of Congress, but that “I’ve got some ideas of my own.”

“Once the people say to Congress, ‘There’s a problem, fix it,’ then I have a duty to say to members of Congress, ‘Bring forth your ideas,’ ” Mr. Bush said. “I clarified a variety of ideas that people should be encouraged to bring forth, without political retribution. It used to be, in the past, people would step and say, ‘Well, here’s an interesting idea,’ and then they would take that idea and clobber the person politically.”

A Social Security specialist at the Heritage Foundation, David John, said the idea is “bad policy” and would not raise enough money to balance the Social Security system, which will begin to pay out more in benefits than it takes in as baby boomers begin to retire in large numbers in the coming decades.

There are various ways the cap could be changed, Mr. John said.

Among the various Social Security plans in Congress, only Senator Graham, a Republican of South Carolina, has proposed increasing the cap to various levels.

Rep. James Kolbe, a Republican of Arizona, has proposed increasing the portion of national wages covered by the tax to 90%, the share that was covered when Social Security was overhauled in 1983. That share has slipped to 85% since then, Mr. John said.

“There is a question of how much of that is a tax hike and how much is correcting an error,” he said of that proposal.

Out of the roughly 14 million Americans who file income tax returns with incomes over $90,000, half earned between $90,000 and $125,000.

“The people who are going to be most affected are going to be the ones who actually feel it. It’s going to make a difference in their lifestyle,” Mr. John said.