The Russian Federal Security Service has searched and interrogated three arms control and nuclear weapons specialists--two Russians and one American--and one of the Russians has been detained, the specialists said today.

Igor Sutyagin, a senior researcher at the Institute for the Study of the United States and Canada, has been taken into custody by the security service, or FSB, a successor of the Soviet KGB. The investigators have been asking questions about a possible leak of classified information, others said.

Sutyagin has not been formally charged, but the other specialists said he has been told he is a suspect in a criminal case, and, after several days of questioning, has been detained in the city of Kaluga, south of Moscow.

A team of FSB agents also interrogated Joshua Handler, a Princeton University researcher who has been gathering material in Russia for his PhD thesis on disarmament in the 1990s. They confiscated a laptop computer, research papers and newspaper clippings, among other things, from his Moscow apartment, Handler said. Eight agents spent seven hours searching his apartment and questioning Handler, who has been affiliated with the U.S.-Canada institute.

The agents also interrogated and seized materials from Pavel Podvig, a researcher and editor of a groundbreaking book published last year on Russian strategic nuclear weapons. Sutyagin contributed a chapter to the book, which was reviewed in advance by the Russian military.

Handler, a one-time Greenpeace activist, said, "Over the last 10 or 15 years of my work, all I have been trying to do is improve U.S.-Russian relations and to encourage greater steps toward nuclear disarmament and to try to improve the international environmental situation and the environment in Russia. I have never sought and never intended harming the security of the Russian federation."

Podvig said neither he nor Sutyagin has done anything wrong.

The searches and detention are reminiscent of FSB arrests and charges against two military men who sought to expose nuclear waste dumping and safety risks by the Russian navy in recent years. The authorities had charged Alexander Nikitin and Grigory Pasko with espionage for revealing what were said to be secrets. Pasko was acquitted of espionage but Nikitin's case is dragging on.