As postal carrier Tyrone A. Frazier was telling FBI agents and Montgomery County police about his harrowing day as the hapless kidnap victim of assassins, a few law enforcement officials were raising a skeptical eyebrow or two.

"We Kept questioning him because, A, his story wasn't plausible and, B, it wasn't corroborated," said one FBI agent.

And, as it turned out, most of what the 31-year-old mailman was telling them apparently had been fabricated.

Arrested and charged yesterday as an accessory to the murder of former Iranian press attache Ali Akbar Tabatabai, Frazier acknowledged late Tuesday night that his abduction tale was untrue, according to FBI officials.

He lied, he eventually told the police, about being hailed along his Northwest Washington delivry route by an unknown black man who forced him, at gunpoint, to turn over his tiny Postal Service jeep.

He lied about having been taken on a wild, hours-long ride about town by two white men he said kept his face down and guns trained at his back.

He lied, police and several reporters discovered, about his address.

Frazier, a part-time jazz musician whose marital problems were reportedly causing him financial as well as emotional problems has now told police and the FBI that he knew Daoud Salahuddin, the black Muslim being sought for Tabatabai's murder, and had agreed to lend him postal jeep in return for $500.

It was Salahuddin, according to Frazier, who suggested that the mail carrier make up the story about being kidnapped and having his jeep stolen by gunmen. He says he cooperated in the arrangement because he was afraid of Salahuddin and because he did not know his postal vehicle was being borrowed to help carry out an assassination.

A woman who told Frazier that Tabatabai had been gunned down by a man posing as a postal carrier said Tuesday that he was shocked and buried his head in his hands.

But the police declined yesterday to comment on whether Frazier was telling the truth on this one point.

Whatever the extent of his advance information, it took seven hours of intense interrogation and "numerous" polygraph tests, police say, before Frazier's initial story began to unravel. By then, according to one FBI agent, Frazier was still in custody and "he wanted to tell the truth."

Showed slides of six black males, one of whom was Salahuddin, Frazier positively identified the bogus mail carrier at 2:46 a.m. yesterday. He then said he had known the alleged assailant since September of 1979.

When the two men met Tuesday morning so that Salahuddin could borrow the jeep, Frazier said Salahuddin showed up dressed as a postal carrier. Getting out of a small blue car, he approached Frazier's jeep. He had his hand in a brown envelope, which Frazier told investigators he though might contain a gun.

After summoning a light blue pickup truck driven by a man Frazier later identified as Horace Anthony Butler, Salahuddin told the mailman to get into the truck. The exchange made, Salahuddin got into the jeep and drove off, said Frazier, who spent the next several hours riding around with Butler.

Frazier also said that Salahuddin had given him a phone number where he could be called should any problem arise over plans to use the jeep. The number, according to the Chesapeake & Potomac Telephone Co., truned out to belong to the Iranian Interests Section of the Algerian Consulate on Wisconsin Avenue NW.

Frazier also gave police the lead that helped them arrest Butler, a self-employed carpenter and black Vietnam veteran, for conspiacy in Tabatabai's murder. It was Butler and not two white men, Frazier said, who drove him to Baltimore and back after his jeep was borrowed. The two men had shared a casual discussion about housing costs and Frazier said Butler gave him his name and address should he ever need any carpentry work done.

The news of Frazier's involvement with the accused Tabatabai assailants came as a shock to friends and residents on his small route.

"He was one of the best men we've ever had," said Elise Aschenbach, who lives in the 3800 block of Cathedral Avenue NW. "He was always neatly dressed. Such a fine man."

Though FBI agents said they doubted that Frazier was a Muslim, as was Salahuddin, Aschenbach and others recalled that he always wore a white crocheted cap -- a "beanie", a neighbor called it -- much like those worn by members of the Muslim faith.

Matthew Allan, the D.C. Department of Recreation's music director, had helped Frazier form a local jazz band called "Heavy Weather" and said he knew that his friend, who played the saxophone, was having financial difficulty.

"He was having marital problems and was talking to lawyers about getting a legal separation," said Allan. "That was taking a toll on him, financially as well as emotionally."

Frzier, according to his father-in-law, George Gross, had been separated from his wife, Sharon, for about a year. The couple had married in 1968 and had a 10-year-old daughter.

Gross said Frazier, a graduate of Spingarn High School who studied music in 1971 and 1972 at Howard University, did not smoke drink or take drugs.

Sharon Frazier said yesterday that she had found out her husband's involvement when she read of it in the newspapers.

"I know less than you and have no comment," she said before hanging up abruptly.

In an account of how he became involved, as described in court records released yesterday, Frazier said he had first met Salahuddin about 10 months ago at the Northeast home of a James Palmore, where Frazier apparently recently lived. He said Palmore, who lived at 1813 Otis St. NE, had introduced him to Salahuddin and that the two men had since seen each other about a dozen times.

A neighbor who lives next door said yesterday that two musicians lived in the two-story house, whose owner she says lives in North Carolina. She said the musicians were named Tyrone and Kenyatta, and she said Tyrone worked at the post office.