The United States has known about the existence of a tunnel system under the new U.S. Embassy in Moscow for years and has "regularly monitored and inspected" it, the State Department said yesterday.

Department spokesman Charles E. Redman, reacting to a story in The Washington Times, said the tunnels were "not a new discovery by any means" and that they were first found and "surveyed" by U.S. personnel prior to 1979, when construction of the eight-building complex began.

Redman said they were "service tunnels" containing water, electrical and sewage pipes and were common in cities built "in {cold} climates such as Moscow."

"The tunnels were physically inspected to our property lines," Redman said. "The portions of the tunnel leading to the new embassy have been controlled since construction began, and they are regularly monitored and inspected."

Redman said the United States realized the tunnels represented a "potential security threat" but said that they were necessary to provide water, sewer and electrical services to the embassy compound.

He said the United States did not know where the tunnels led outside the compound's property lines.

The Times said the tunnels, the largest 10-feet high, appeared to be part of the eavesdropping system set up by the Soviet KGB to penetrate embassy security. It said the tunnels led to an adjacent church thought to be used by the Soviets as their center for espionage activities against the embassy.

Redman said the U.S. government did not have any "firm information" that any of the tunnels led to the church and described reports to this effect as "speculation."

A counterintelligence expert outside the administration said the use of tunnels to try to penetrate the security of U.S. embassies was a standard technique used by Soviet bloc and Chinese intelligence services and that the U.S. government was aware of this.

He said various measures, such as building barriers inside any tunnels found, were used to counter such efforts and noted that the proposed new annex at the U.S. Embassy in Moscow would be built on stilts to insulate it from attempts at underground penetration.

The administration stopped construction in 1985 on the new Moscow embassy's chancery, which is its main office building, after it discovered the Soviets had implanted devices in the walls and floors to monitor conversations and gain access to classified information.

A recent report prepared by former defense secretary James R. Schlesinger on security problems at the new chancery proposed that the top three floors be rebuilt completely and a new eight-floor annex be constructed to assure the security of embassy telecommunications and classified information.