WASHINGTON -- President Bush's claim that he has a legal right to eavesdrop on some U.S. citizens without court approval has widened an ideological gap within his party.

On one side is the national-security camp, made even more numerous by loyalty to a wartime president. On the other are the small-government civil libertarians who have long held a privileged place within the Republican Party but whose ranks have ebbed since the 2001 terrorist attacks.

The surveillance furor, at least among some conservatives, also has heightened worries that the party is straying from many of its core principles the longer it remains in control of both the White House and Congress.

Conservatives have knocked heads in recent months over the administration's detainment and treatment of terrorist suspects, and as recently as yesterday over provisions of the Patriot Act. Strains also have grown among conservatives over government spending and whether to loosen U.S. immigration rules.

But the current debate over using the National Security Agency for domestic surveillance -- which the administration has defended as legal and necessary -- hit a rawer nerve because it pits national-security concerns against a core constitutional right, in this case, the Fourth Amendment right against unreasonable searches and seizures.

"It seems to me that if you're the president, you have to proceed with great caution when you do anything that flies in the face of the Constitution," said Warren Rudman, a former Republican senator from New Hampshire who has served on a number of government intelligence advisory boards. He calls the administration's surveillance program "a matter of grave concern."

Since 1978, Congress has required the executive branch to seek warrants through a secret federal court for domestic eavesdropping on foreigners or U.S. citizens suspected of terrorism or espionage. Such permission is all but automatic and usually is granted within hours. The court granted warrants at the rate of almost five a day last year -- and rejected none.

President Bush and his top aides argued this week that they were on solid legal ground in ordering -- without going through the secret court -- large-scale eavesdropping of communications between the U.S. and other countries to thwart potential terrorist attacks. They claim they had the authority to conduct the spying under the president's powers as commander in chief, as well as under a congressional resolution that approved the use of force in Afghanistan in 2001.

Yet some prominent conservatives reject that argument. Some even have accused the administration of treading on the Constitution and stretching the prerogatives of the presidency to the detriment of balanced government.

David Keene, chairman of the American Conservative Union, described the spy program as a case of "presidential overreaching" that he said most Americans would reject. Columnist George Will wrote in a Washington Post opinion piece that "conservatives' wholesome wariness of presidential power has been a casualty of conservative presidents winning seven of the past 10 elections."

Bob Barr, a Georgia conservative who was one of the Republican Party's loudest opponents of government snooping until he left Congress in 2003, says the furor should stand as a test of Republicans' willingness to call their president to task. "This is just such an egregious violation of the electronic surveillance laws," Mr. Barr says.

Sen. Arlen Specter, the Pennsylvania Republican who chairs the Judiciary Committee, has called the program "inappropriate" and promised to hold hearings early next year. Republicans joining him include centrist Sens. Chuck Hagel of Nebraska and John Sununu of New Hampshire, along with limited-government types like Larry Craig of Idaho.

The three, along with Sen. Olympia Snowe of Maine, have sided with Democrats in the Patriot Act fight, citing concerns the government is running rough-shod over civil liberties in the name of the war on terrorism. Without Senate approval by Dec. 31, a bulk of the law's key provisions would expire. Negotiations over a compromise continued yesterday.

Some other top Republicans have defended the president's right to conduct surveillance outside congressionally mandated rules. Sen. Trent Lott of Mississippi summarized the argument: "I want my security first," he told reporters when news of the program broke last week. "I will deal with all the details after that."

Prominent neoconservatives William Kristol and Gary Schmitt opined earlier this week that the president has the authority to collect foreign intelligence "as he sees fit," even within the U.S. And no matter how much people might wish it, they wrote, "Congress cannot legislate for every contingency."

Vice President Dick Cheney portrayed the dispute as one entirely about presidential power. "I believe in a strong, robust executive authority, and I think that the world we live in demands it," he told reporters while traveling abroad on Tuesday.

Some conservative critics contend that the fault lines within the party are easy to trace. As with so much else, they say, the trail leads to Iraq.

"From the beginning, the folks who thought it was a good idea to go into Iraq have found good reason to think that all other Bush policies, from torture to domestic surveillance, are justified," said Robert Levy, a conservative legal scholar at the libertarian Cato Institute. "This is just one in a litany of ongoing events that have separated the noninterventionist wing of the Republican Party from the neocon wing."

--Anne Marie Squeo contributed to this article.

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