The KGB secret police announced today that they have arrested a man for setting off an explosion in Moscow, a rare disclosure of urban terrorism in the Soviet Union.

The announcement, transmitted by Tass news agency, said that the bombing took place June 11 in a taxi outside the Sovietskaya hotel, which is often used by foreign dignitaries.

Tass said the arrested man, who was not identified, confessed that he had committed the crime out of "vile motives."

"An investigation is continuing," Tass said.

The alleged explosion at the Sovietskaya, which is on a main thoroughfare near the center of the city, went unreported in the controlled Soviet press at the time.

In January an explosion was reported to have taken place on Moscow's sprawling subway system. Official Soviet sources blamed that blast on terrorists, but authorities have never announced whether any arrests were made.

Such act of violence are rarely publicized in the Soviet Union and even the brief Tass announcement was considered extraordinary.

There were no other details in the Tass report, but an employee of teh Moscow taxi administration told reporters that the explosion occurred when a texi driver opened his trunk. He said the driver was injured in the incident but is now back at work. The emplyee said property damage was "insignificant."

The administrator of the hotel, reached by telephone, said she was unaware of the blast, "and even if I did I could not tell you because we do not release such information."

Moscow police headquarters said it was not even aware the blast had taken place.

Meanwhile, Soviet scientist Benjamin Levich told reporters in London over the telephone from Moscow today that his leaving the Soviet Union is "a question of death or life."

Levich, a Jewish sceintist who has made important advances in the highly technical field of physiochemical hydrodynamics, is being honored next week with a 60th birthday conferences sponsored by leaders of Western science.

He applied for a visa to emigrate to Israel in 1972 and has been offered professorships in many Western nations, but has been refused permission to leave the country.