The postman accused of aiding the assassin of prominent exile Ali Akbar Tabatabai in Bethesda last summer was charged with bribery yesterday in federal court after the Montgomery County case against him collapsed.

The federal warrant charged that Tyrone Frazier, 31, took $200 and the promise of $300 more for the use of his postal jeep in the Tabatabai murder plot last July 22.

Frazier had been indicted in Montgomery County on charges of being an accessory to the Tabatabai slaying, and of lying to a policeman. But a Montgomery Circuit Court judge ruled on Thursday that the statement Frazier gave to police the morning after the slaying could not be used in court because FBI agents induced him to change his story by promising special treatment.

Frazier first told authorities he had been kidnaped on the day of Tabatabai's slaying and his Postal Service jeep stolen by a gunman. After several hours of questioning, he acknowledged taking part in the assassination plot, police said.

Calling the statement "the single most probative piece of evidence which we had hoped to use at trial," Montgomery County State's Attorney Andrew Sonner yesterday dropped the state case against Frazier.

Tabatabai, former press attache to the Shah of Iran, was gunned down in the doorway of his split-level Bethesda home on July 22 by a man posing as a postman.

Daoud Salahuddin, the alleged killer, is believed to have fled to Iran. Authorities say the search for him is continuing.

Since the state charge against Frazier carried heavier penalties than the bribery case -- a death sentence was possible -- authorities decided at the time to charge Frazier in Montgomery County. But when that case was dropped, federal authorities pressed the bribery case, FBI spokesman Lane Bonner said.

Conviction on the bribery charge carries a maximum penalty of 15 years in prison, a $20,000 fine and the loss of Frazier's federal job with the U.S. Postal Service.

Also, yesterday, a Montgomery County judge refused to reduce the $100,000 bond set for Horace Butler, another defendant in the Tabatabai case.

Butler, who allegedly drove Frazier around for several hours while the murder plot was being executed, faces Montgomery County charges of conspiracy to commit murder and being an accessory to a homicide.