WASHINGTON — Even as he has faced the defeat of domestic priorities and growing opposition to the U.S. engagement in Iraq, President Bush has always been able to rely on one great asset: broad political support for his conduct of the struggle against terrorism.

But now, four years after Sept. 11, concerns are rising even among fellow Republicans over some of the tools he is using in that effort, and Bush finds himself defending the very war that defined his presidency and assured his reelection.

Bush's surprising admission Saturday that he had ordered domestic communications surveillance without court approval came as Republicans once willing to give the White House wide legal berth on security matters have begun to call for greater scrutiny of U.S. conduct.

Republican lawmakers have in recent days rebuked the White House in its opposition to an all-out ban on torture — forcing Bush to capitulate — and have demanded information on a newly revealed network of secret CIA prisons around the world. At the same time, the Republican-led Senate refused Friday to renew the Patriot Act, expressing growing concern about the anti-terrorism law's effect on civil liberties.

The unease within his party — and the specter of hearings on Capitol Hill on some of the anti-terrorism tactics used — suggests the national debate is beginning to shift on how much latitude Bush can claim in the name of national security.

Bush has scheduled a nationally televised address tonight from the Oval Office to extol the recent success in Iraq, primarily last week's parliamentary elections, but the newly intense questions about his administration's conduct presents a potentially complicated challenge.

Just when White House strategists had hoped to begin rebuilding his sagging public approval ratings, Bush must continue arguing that Iraq is a central front in the war on terrorism and he must defend the very nature of that broader war. Bush must make these arguments in the face of criticism not just from Democrats and liberal groups, but from Republicans and some conservatives.

"There was something about an unprecedented threat that led the administration to do some extraordinary things and led others not to question what they were doing," said Jon B. Alterman, director of the Middle East program at the Center for Strategic and International Studies. "But we're four years after Sept. 11, and the problems are more complex. People have gotten over the initial shock of things, and there's a desire to address issues in a more complex and more nuanced way, which the president has not often been willing to do in public."

Bush has not hidden his frustration with his new predicament.

On Friday, he tried to change the line of questioning during an interview by PBS' Jim Lehrer when the news anchor suggested that the revelation of National Security Agency surveillance of domestic calls was the "main story of the day."

"It's not the main story of the day," Bush said. "The main story of the day is the Iraqi election."

The president then refused to discuss the matter. "Just not going to do it," Bush said, arguing that discussing such methods would "compromise our ability to protect the people." But White House strategists clearly changed their minds, concerned that they once again may have landed on the wrong side of public opinion — and of their once-forgiving compatriots on Capitol Hill.

Bush aides, huddling late Friday with intelligence officers, decided they needed to respond — hoping to reframe the dialogue in a familiar way by painting administration critics as giving comfort to the enemy.

"We are directly taking on critics," said a senior administration official who spoke on condition of anonymity because the matter related to internal strategy discussions. "Democrats now face a choice — defend a position that would put our security at greater risk or support our efforts to protect Americans."

As part of the White House's response, Bush is likely to seize on the recent report by the bipartisan Sept. 11 commission giving failing grades to the government for its work to protect the U.S. from another attack. Democrats had cited that report as evidence that Bush had failed to secure the U.S. But White House officials will turn that argument around, citing their aggressive tactics as proof of administration efforts to fulfill the commission's demands for more action.

So, 48 hours after Bush stunned many with his capitulation to onetime rival Sen. John McCain (R-Ariz.) in accepting an unequivocal ban on torture, the president used a rare live radio address from the Roosevelt Room of the White House to confirm that, indeed, he had ordered the NSA to monitor some phone calls and e-mails.

He called opponents of extending some parts of the Patriot Act "irresponsible," and defended his use of exceptional measures since Sept. 11, 2001, as part of his role as commander in chief.

But Bush was clearly on the defensive Saturday. And despite arguing that Americans "expect me to do everything in my power under our laws and Constitution to protect them and their civil liberties," he faced the prospect of an increasingly restive Republican Congress.

Sen. Arlen Specter (R-Pa.), chairman of the Senate Judiciary Committee, pledged to hold hearings on the NSA order. Some Republicans strongly questioned how citizens' privacy rights would be protected if government agencies could conduct electronic surveillance of citizens without a court review.

Conservatives such as Sen. John Sununu (R-N.H.) argued that the Patriot Act, which gives investigators an assortment of additional tools, violates the very tenets of personal freedom that have defined American values from the founding of the country. Sununu and others complained that about 30,000 "national security letters" had been issued under the law and recipients were prohibited from discussing the letters.

Although polls suggest the public remains supportive of government vigilance against terrorism, many Republicans are wary that — at the outset of the 2006 midterm election season — Democrats could paint certain methods as violations of traditional American values.

"We need to be mindful of Ben Franklin's words over 200 years ago: Those who would give up essential liberty in the pursuit of a little temporary security deserve neither liberty nor security," Sununu said Friday. And he noted that the administration had not responded to requests to work out their differences.

The administration's attempt to exclude CIA agents from a ban on torture has caused a particular backlash.

Many Republicans responded to arguments by McCain, a potential presidential contender, that some U.S. approaches to combating terrorism have damaged the country's image and moral authority on the world stage.

Laura Donohue, a fellow at Stanford University's Center for International Security and Cooperation, said the White House was unlikely to reverse course.

She said the president enjoyed broad powers to take aggressive action, thanks to a series of congressional actions and executive rules that were not easily changed — and that even GOP leaders raising concerns now might fall back into line should terrorists strike again.

"In one sense it's encouraging that people are starting to realize what has been going on," Donohue said. "But I can't help but question, if there's another attack, how will these same people respond? Will they put in checks and balances to ensure that we have the information that we need for state security without gross violations of individual rights? Or will they roll over and allow the executive unchecked power?"

Bush will have ample opportunity to make his case for continued executive power to fight terrorism.

But, after a series of speeches designed to boost support for the Iraq war, and as he prepares to hit the airwaves tonight, this was not the debate White House officials had expected for the new year.

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