Postal carrier Tyrone A. Frazier was midway through his routine delivery route in Northwest Washington yesterday when he suddenly was flagged down by a man for what was the beginning of a harrowing day that found Frazier the innocent tool in an assassination plot.

When Frazier regained his freedom five hours later, he was so frightened that he hid in an office of a junior high school for 30 minutes waiting for police to rescue him, fearing to even venture into a hallway for a sip of water.

One of Frazier's kidnaper's, a black man wearing a postal uniform who hailed Frazier at Massachusetts and Idaho avenues NW about 11:15 a.m., was identified later by police as the gunman who killed Iranian activist Ali Akbar Tabatabai.

Police said Frazier's kidnapers, the black man and two whites, forced Frazier into their vehicle.Then the two white men kept Frazier face down with guns trained on him and took him on a rambling ride. The black suspect then used Frazier's Postal Service jeep to pose as a carrier with two special-delivery letters for Tabatabai's home, police said.

The complete story of Frazier's hours-long odyssey remained unclear late last night because Federal Bureau of Investigation agents continued to hold him for questioning. Police said Frazier was not a suspect.

Officers would say only that Frazier had been taken at gunpoint in Washington and released near Sligo Junior High School in Silver Spring about 4 p.m. after being driven around parts of the Washington area. He was neither bound nor blindfolded during his ordeal but was guarded continuously by the two white men.

It was about 4:15 p.m. when a dazed, shaken Frazier wandered into the lower-level office of the English language center at the school at 1401 Dennis Ave.

Adelia Wheeler, a coordinator of the program for non-English speaking students, said Frazier, dressed in the short pants that are part of the summer uniform of the Postal Service, quietly asked if he could use the telephone to call his Postal Service supervisor.

As Wheeler listened, Frazier unfolded the harrowing tale, obviously unaware that he had been used in a killing. He said his captors, only instructions upon releasing him a short distance from the school was, "do not turn right.?

When he hung up, Mrs. Wheeler told Frazier of the news of the assassination and as the mailman came to understand his unwitting role in it, he buried his head in his hands on a table.

"He was very interested, to say the least." Mrs. Wheeler said last night.

She said Frazier repeated that he "wasn't scared, but I was afraid."

Frazier had no idea where he was, Mrs. Wheeler said, so she showed him the location of the school on a map.

"It was amazing to him," she said. He told her of being driven through a woods in the back of a truck. "I think he said three men was holding him," Mrs. Wheeler said.

Frazier at one point while waiting for police, said he was thirsty, but feared going into the hallway to a fountain only steps from Wheeler's door. "He asked if it would be safe to get water in the hall. I said it'll be okay. So he did.

"He obviously had undergone considerable emotional shock," Wheeler said.

Frazier dashed out Wheeler's door when he heard several plainclothes policemen shouting, "Frazier, Frazier." Wheeler said. "They came and left so fast," Wheeler said that she wasn't sure they were policemen. "I hollered at them and asked if the local police had been notified. They said 'yes' and left."

A coworker of Fraziers at the Friendship station, William Branison, said he saw Frazier yesterday morning.

Branison, who works as a collector at the station, said it was roughly 11 a.m. when he saw Frazier walking in the 3800 block of Massachusetts Avenue NW.

The shooting occurred about five miles from Frazier's route, which covers the 3800 blocks of Massachusetts, Cathedral and Wisconsin avenues, the 2900 blocks of Bellevue Terrace and 38th Street, and the 3200 block of Sutton Place.

Carriers who work out of the Friendship station deliver mail in the 20016 zip code area, which includes portions of Northwest Washington and Bethesda, but the area of the shooting is serviced by carriers from the West Bethesda postal station on Seven Locks Road.

Frazier, who is married and a father of a 6-year-old daughter, is a jazz musician who recently played trumpet with a group called "Heavy Weather," which appeared at the old Hollywood Club at 9th Street and Florida Avenue NW.

Frazier attended Howard University, where he was active in musical groups.

Until about two months ago, he and his family lived in a town house south of Alexandria, near Fort Belvoir.