he rush has already begun to "unshackle" the Central Intelligence Agency and its fellow spy agencies so that they can better combat terrorism. Some easing of restrictions may be warranted in light of last week's terrorist attacks on New York and Washington. But any changes must be carefully weighed by the Bush administration and Congress. The temptation will be great to take steps, including loosening limitations on domestic spying, that could end up compromising important democratic principles without yielding any tangible gain in the fight against terrorism.

Generally, there are fewer restraints on intelligence agencies than popularly assumed, especially when it comes to antiterrorism. The C.I.A., for example, is not barred from recruiting foreign informants with criminal records or a history of involvement in terrorist activities. The recruitment of such people simply has to be approved by senior intelligence officials and there has to be an expectation that the source will produce valuable information.

We would be surprised if these guidelines were the reason there was no warning about last week's attacks. The more likely explanation is that intelligence agencies, with White House and Congressional concurrence, have neglected the cultivation of foreign informants in recent decades in favor of valuable but extremely expensive technical collection systems like spy satellites. These technologies, which can intercept millions of intercontinental phone calls and show a license plate from 200 miles out in space, have served the nation well. They cannot, however, tell the president what Osama bin Laden said yesterday to his henchmen in a mud hut in the mountains of Afghanistan.

After last week's assaults on the World Trade Center and the Pentagon, the president and his aides may also understandably want to know what terrorist conspirators are saying to one another in the United States, either in person or over the phone. If communications between just a few of the suicidal hijackers had been intercepted in the days before the attack, perhaps the plot could have been foiled. Obtaining that sort of information involves difficult legal and technical issues that cut directly to Fourth Amendment protections against unreasonable searches and seizures.

The business of tracking down terrorists in the United States belongs primarily to the Federal Bureau of Investigation and other law enforcement agencies, which may now need additional money and staff. With a court order, the F.B.I. can tap specified telephone lines, intercept mail and take other measures to track the activities of suspected terrorists. Attorney General John Ashcroft is seeking expanded wiretap powers for the bureau. Even with that enhanced authority, the F.B.I. would still lack the technology and statutory right to randomly monitor telephone communications within the United States ?including cellphones ?in hopes of intercepting information about terrorist plots.

The organization that has the technology to do some of that, the National Security Agency, is limited by law and executive order in monitoring communications within the United States. To target the communications of a suspected terrorist in the United States, the N.S.A. must seek the approval of a special federal court, and show probable cause that the suspect is an agent of a foreign power and is involved in terrorism, espionage or sabotage.

These rules were established in 1978 by the Foreign Intelligence Surveillance Act. There are now bound to be efforts to rewrite that law to give the N.S.A. greater latitude. Some refinement may be possible, but even the most modest change will require the utmost care by the White House and Congress to ensure that this kind of highly intrusive and indiscriminate intelligence gathering is tightly controlled and not subject to abuse.

Other intelligence issues, including the ban on assassinations, will doubtless be revisited in the days ahead. The pressure to relax restrictions is nearly overwhelming, but the nation will not be well served if there is a stampede in Washington to discard restraints that were carefully put in place to reflect and to protect the character and principles of American democracy.