Russian security services have charged an arms control researcher with spying for the United States, sources said today.

Igor Sutyagin, chief of the section on military technological research at the Institute for the Study of the United States and Canada, was detained Oct. 27 by the Federal Security Service in Kaluga, south of Moscow, where he lives.

At the time, sources said the investigation was looking into leaks of classified information. But on Nov. 5, Sutyagin was formally accused of espionage, the sources said. Details of the charges are not known.

Paul Podvig, editor of a book on Russia's nuclear forces to which Sutyagin contributed a chapter, said, "I am 100 percent certain that Igor didn't do anything wrong."

According to the sources, the security services searched Podvig's office for a second time recently and seized between 500 and 600 copies of the book, "Russian Strategic Nuclear Forces," which was published last year.

Sergei Rogov, director of the USA-Canada Institute said there was no access to secret information at the institute.

"This is a very unpleasant situation," Rogov said. "Unfortunately, previously our institute was a couple of times in the same situation, and a couple of employees of the institute admitted that they were sending information back to the CIA, and they are in the United States now, with a formal status as someone who suffered because of cooperation with the CIA.

"It's very unfortunate that this institute, against our will, was involved again in this kind of game. Naturally, only the court can decide whether the accusations against our researcher are true or not. Only at the trial can they find out if he is guilty or not.

"Right now he is under investigation and it doesn't make our work easier, because dealing with controversial subjects like arms control, it's easy to be accused of selling out, especially when you think about an agreement when both sides have to make concessions, which originally may be perceived as impossible," Rogov said.

Joshua Handler, a Princeton University PhD student who was a guest at the USA-Canada Institute, was questioned in the case, but no accusations have been made against him. He recently left Russia.