THE THOUGHT SPREADS in some quarters that if a terrorist turned up in a country where he thought he was safe, it would be just fine for American commandos to go in and grab him. The Israelis did it with Adolf Eichmann and were widely applauded, or at least understood. But could the United States do it today?

Legally, that a defendant was kidnapped from a foreign country would be no bar to prosecution. If someone could snatch a plane hijacker or a gunman who had murdered an American ambassador, smuggle him onto an airplane and fly him to the United States, the terrorist could be tried for a violation of American law and sentenced severely. That might make a lot of Americans feel better. But the legal ramifications of this action are sobering.

It is not simply that the country in which the kidnapping took place, even a friendly country, would react in outrage. An unfriendly country, especially one that had already shown a disposition to target Americans, might respond in kind. Libyans might kidnap an American official who had been engaged in planning the recent bombing raids and hustle him back to Tripoli for trial. There is also a potential for civil liability. Assistant Attorney General Stephen Trott points out that U.S. officials cooperating in an abduction or in a subsequent trial have been personally sued by the defendant.

A further legal question: what would be done if the country that had harbored a terrorist demanded that the United States extradict his kidnappers for trial? Bounty hunters kidnapped a man in Canada and brought him home for trial not long ago. The Canadians, furious, sought the extradition of the bounty hunters, who were subsequently sent across the border, tried for kidnapping and convicted.

Abduction is not a sensible way to combat terrorism. It opens a Pandora's box of problems with other countries and diminishes the American claim to be dedicated to upholding the rule of law. Fortunately, there is another way. Extradition treaties with friends can be strengthened so that international terrorists will not escape prosecution by claiming their crimes are political acts. Economic and diplomatic pressures can be brought to bear on those nations that harbor and support terrorists and then neither extradite nor try them. These steps are slower than kidnapping, and perhaps not so emotionally satisfying. A country that asks others to act within the context of the law, however, has a special obligation to do so itself.