he Constitution does not give the government sweeping emergency powers to limit civil liberties. But legal experts say the courts have effectively ceded to the government vast powers to limit many freedoms when the nation's security was threatened in the past.

As a result, the debates in Washington and state legislatures about limiting civil liberties to battle terrorism could be decisive because many of the new limits may never receive rigorous court review.

"The courts have always interpreted the limits on government action much differently during times of national crisis," said Michael C. Dorf, a professor of constitutional law at Columbia Law School. "So as a matter of practical fact, the government has emergency powers."

Attorney General John Ashcroft is pressing Congress for a series of new anti-terrorism laws, including measures that would expand electronic surveillance and the search powers of law enforcement officials. In New York, Attorney General Eliot L. Spitzer has called for a law expanding wiretap authority, and the State Senate passed such a bill on Monday. Other states are expected to consider similar measures.

While courts will retain the power to hear challenges to any restrictions on civil liberties that are part of the new laws, lawyers say the president's martial language and popular sentiment will prompt judges to defer to government officials in their reviews of such measures as expanding wiretapping efforts.

History is full of examples of the courts approving limits on civil liberties when the country was perceived to be in danger.

"The greater the threat, the greater the leeway the courts will give government," said Peter H. Schuck, a professor at Yale Law School.

In one case that arose in World War I, a group of Socialists were arrested for distributing pamphlets that urged peaceful opposition to the draft. The demonstrators were tried and convicted under the Espionage Act, which included provisions barring efforts to obstruct enlistment in the armed forces.

The arrests were upheld by the Supreme Court in 1919, which issued a landmark opinion by Justice Oliver Wendell Holmes Jr., who was often a champion of First Amendment freedoms. During war, he wrote, statements that might be protected in ordinary times could be barred.

"The most stringent protection of free speech," Justice Holmes wrote, "would not protect a man in falsely shouting fire in a theater and causing a panic."

In an atmosphere of cold war anxieties in 1951, the Supreme Court approved the conviction of leaders of the Communist Party for advocating the overthrow of the government.

The opinion concluded that the need to bar even threats of violence against the country was "a substantial enough interest" to limit First Amendment freedoms.

Some precedents approving limits on civil liberties are now widely viewed to have been constitutional errors that would not be repeated today. Many legal experts say the Supreme Court's approval of the internment of Japanese-Americans during World War II has been discredited. They say courts would now strike down any such categorical measures against Arab-Americans that might be contemplated.

But some lawyers say the more extreme court decisions of the past show how easily judges can be swept up in a warlike mood. "Those cases are now seen as mistakes," said David Cole, a professor at the Georgetown University Law Center. "But we repeat our mistakes rather than learn from them."

Some constitutional experts say the public in recent decades has come to view many civil liberties ・like the right to exchange political views ・as central to American life.

For that reason, some experts say courts might now be more willing to be critical of the government than they have in the past.

Erwin Chemerinsky, a constitutional law expert at the University of Southern California, said the Supreme Court's decision in the 1971 Pentagon Papers case showed that modern courts could be independent of government officials. In that case the court refused the government's request to block publication of secret revelations about the Vietnam war for reasons of national security.

Justice Potter Stewart wrote that publication could be stopped only if it would "surely result in direct, immediate and irreparable damage to our nation or its people."

That test might be met by some of the measures now being considered, like intercepting computer communications among suspected terrorists. But Mr. Chemerinsky said he thought the courts would not rubber- stamp more extreme measures. Wholesale strip searches at airports, he said, would probably fail in the current Supreme Court.

"This court is institutionally deferential," Mr. Chemerinsky said, "but I don't think this is a court that will say, `Anything goes.' "

But other constitutional law experts said the current justices would be influenced by the atmosphere of war.

Randolph M. McLaughlin of Pace University Law School in White Plains said the debate in the coming weeks about what measures were necessary to protect the country might be the last meaningful debate on the issue.

"This Supreme Court," Mr. McLaughlin said, "will ratify the laws that are passed during this period."