The U.S. Embassy in Moscow was secretly bugged by the Soviets for a year and possibly longer by sensing devices capable of picking up what was written on embassy typewriters, administration officials confirmed last night.

CBS News reported that the bugging was a "sophisticated electronic spy operation which gave Soviet leaders an inside look at what U.S. diplomats were doing and planning."

Correspondent David Martin said Soviet agents secretly installed tiny sensing devices in about a dozen embassy typewriters. "The devices picked up the contents of documents typed by embassy secretaries and transmitted them to antennas hidden in the embassy walls," he reported.

An informed administration official confirmed that the embassy had been "penetrated" by "lifting things off typewriters. No doubt about it." The offical said the bugging was discovered some time ago and had been stopped.

CBS reported that the antennas in the embassy walls "relayed the signals to a listening post outside the embassy. The typewriters were in use from 1982 until the operation was uncovered in 1984."

The network also reported that intelligence experts think that Moscow was running a version of the same operation earlier, citing an antenna discovered in cleaning up after a 1978 fire.

CBS said that U.S. officials do not know exactly how the bugs were installed and that they might still be in place except for a warning from a friendly government "whose own embassy had been the target of a similar eavesdropping operation."