The FBI accused a Russian diplomat of espionage yesterday, one week after Russian authorities detained and ordered the expulsion of an American diplomat in Moscow on similar grounds.

U.S. officials said Stanislav Borisovich Gusev, a second secretary at the embassy here, was caught outside State Department headquarters while collecting information transmitted from a listening device planted in a high-level conference room on the seventh floor. That is the most secure part of the building, where Secretary of State Madeleine K. Albright and other top officials have their offices.

Gusev was held briefly by the FBI and then turned over to the Russian Embassy because he claimed diplomatic immunity, the U.S. officials said. The State Department said Gusev had been declared persona non grata and must leave the United States within 10 days.

While U.S. officials formally denied that the arrest was in retaliation for the incident in Moscow, it clearly followed the pattern of tit-for-tat espionage cases that were common during the Cold War but have been rare since the breakup of the Soviet Union in 1991.

Last week, Russian authorities briefly detained Cheri Leberknight, 33, a second secretary in the U.S. Embassy in Moscow. Alexander Zdanovich, a spokesman for the Federal Security Service, one of the successor organizations to the Soviet KGB, said Leberknight was "caught red-handed trying to get from a Russian citizen documents on military and strategic information classified as state secrets." She was quickly turned over to U.S. officials in Moscow but was ordered to leave the country within 10 days.

After Gusev was detained yesterday afternoon, Undersecretary of State Thomas R. Pickering summoned Russian Ambassador Yuri Ushakov to the State Department and lodged a protest, just as the Russian Foreign Ministry did with U.S. Ambassador James F. Collins in Moscow last week.

A Russian Embassy official said Gusev had been working in Washington for about a year. The embassy had no other immediate comment.

U.S. officials said Gusev's apprehension resulted from a long counterintelligence investigation by the FBI, which cooperated with the State Department Diplomatic Security Service in finding the bug on the seventh floor using electronic gear.

"This is an example of good, solid, standard counterintelligence by the FBI," one U.S. official said. "The FBI observed him outside the State Department on several occasions. It became apparent what he was doing."

Another senior official said, however, that there was cause for concern about a possible high-level security breach. "The larger issue here is, if they were able to get that device in there, what else is in the building and what is the State Department going to do about it? That is a huge issue," he said.

The detention of Leberknight, the American diplomat in Moscow, came shortly after the announcement that a U.S. naval code clerk, Daniel King, 40, had been arrested for passing secrets to Russia in 1994. King had been assigned to the National Security Agency in Fort Meade, Md., and he allegedly mailed a computer diskette containing classified information to the Russian Embassy.

Staff writers Steven Mufson and Walter Pincus contributed to this report.