The Soviet news agency Tass tonight challenged published reports that Maj. James R. Holbrook, former assistant U.S. Army attache here, was a victim of a Soviet blackmail plot last month and instead accused him and a colleague of drunkenness and sexual promiscuity.

In recent years, the Soviets have printed numerous attacks on U.S. diplomats, usually selecting a few each year for official denunciations as spies.Today's mudslinging response goes beyond customary denunciations and shows anew the official ire felt here against the Reagan administration, which has accused the Soviets of violating international rules of conduct and seeking world domination.

The Tass account alleged that Holbrook and Lt. Col. Thomas Spener were caught in a compromising situation with a Russian woman at a hotel in Rovno, in the Ukraine, on Jan. 14 by "hotel staff and militiamen." Tass said press reports that two Americans "had had narcotic drugs added to their drink is refuted by their own restaurant bill."

Holbrook had been sent back to Washington Jan. 17 after reporting that Soviet security agents had tried to blackmail and recruit him in Rovno, according to reliable sources. They said the effort included Soviet attempts to photograph Holbrook in compromising circumstances. The sources said that Spencer and Holbrook may have been drugged. The State Department, which first refused comment, later said it had filed a protest over the incident.