Soviet secret police last month sought unsuccessfully to blackmail and recruit as a spy a U.S. Army attache stationed in Moscow who is a candidate to be a military adviser to Vice President Bush, a position in which he would have access to high national secrets, reliable sources say.

The sources said the attempt to recruit Maj. James R. Holbrook may have included use of drugs to incapacitate him and a military colleague, efforts to arrange compromising photographs of Holbrook and an offer of "help" from a Soviet colonel whom Holbrook knew from a previous Eastern Bloc assignment and who mysteriously appeared on the scene at a crucial moment.

The U.S. Embassy here has refused all comment on the incident, which the sources described as the most serious -- although crude -- attempt to compromise and recruit a U.S. Embassy staffer in Moscow in recent years. The attempt failed when Holbrook and his traveling companion, Army Lt. Col. Thomas A. Spencer, immediately reported the setup to their superiors, the sources said. Holbrook since has returned to Washington with his family.

Holbrook, contacted at his suburban Washington home, refused to discuss the incident, saying he was told "by our PR guys that this is an obvious no comment situation. I can't tell you anything." A State Department spokesman refused to comment, saying, "We cannot confirm or deny the story."

[Peter Teeley, press secretary for Bush, said Holbrook was one of four persons recommended by the Army for the job of special military adviser to the vice president. He said no action has been taken on Holbrook's or the other nominations and the job is so far unfilled.]

Sources here said the entrapment attempt occurred in western Ukrainian city of Rovno, apparently, shortly before Washington ordered Holbrook home for an interview for the job with Bush.

Observers speculate that Soviet intelligence may have learned that Holbrook was a prospect for the position with Bush, where he could have access to sensitive Reagan administration secrets, sit in on military strategy sessions and see highly classified information of the United States and its allies.

Holbrook, 41, a career officer highly regarded by the foreign community here as a Soviet affairs specialist with perfect command of Russian, had been in Moscow since April 1979. He was transferred back to Washington on Jan. 17, sources said. Spencer is still assigned to the embassy.

Sources said the incident occurred the week of Jan. 12, when Spencer and Holbrook went to visit Rovno and Lvov, the Carpathian military district headquarters city. Both are near the Polish border, and U.S. officials have been attempting to determine the state of Soviet military readiness in that region.Soviet secret police closely follow and watch foreign attaches on such trips.

While the two were in Rovno, the sources said, Spencer was taken ill, possibly having been drugged, and he and Holbrook became separated. Attaches always travel in pairs because of the dangers inherent in being alone under constant close scrutiny by Soviet agents.

The sources say Holbrook then became the target of an entrapment attempt that centered on efforts to get compromising photographs of him.

At this point, sources said, a Soviet colonel whose identity is unknown but who was said to have been acquainted with Holbrook from an earlier assigment in Potsdam, East Germany, intervened with the recruitment attempt.

Holbrook is said to have flatly turned the Soviets down. Some sources said that for several tense hours, the Soviets pressured the isolated Americans and refused to allow them to communicate with the embassy or to leave Rovno.

The embassy's tight lid on information about the incident has ruffled other foreign attaches who want to be briefed so they can guard against the same thing happening to them.

The last known major drugging incident occurred in 1968 when a British and an American officer were reportedly drugged during a trip to Moldavia. They recovered in their rooms and returned to Moscow.