A Washington man who worked for Ayatollah Ruhollah Khomeini's diplomatic representatives here was charged yesterday with murdering Ali Tabatabai, an outspoken Iranian exile who was gunned down at the doorway of his Bethesda home Tuesday.

The suspect, Daoud Salahuddin, 29, has belonged to an orthodox Muslim sect in Washington for several years and worked as a security guard for the Iranian Embassy here earlir this year, according to associates.

Salahuddin, also known as David Belfield, was still being sought by FBI agents and Montgomery County police last night.

An Iranian who witnessed the slaying was the first person to identify Salahuddin tentatively as the assassin, according to a sworn statement filed in federal court by FBI agents.

The statement adds that the Iranian witness, Seyed Ali Mortazavi, was shown 400 photographs "taken during the course of surveillance activities of a Black Muslim sect which has been the target of intensive investigation for several months." The group under surveillance was a cadre of Muslims known as the Islamic Guerrillas in America, according to police sources.

Two other men were arrested yesterday and charged with conspiracy in connection with the murder -- including a D.C. postman who told police he had been offered $500 by Salahuddin for use of his postal jeep in the plot.

The postman, Tyrone Anthony Frazier, originally told police he was abducted at gunpoint by three men who seized his postal jeep. But during a 10-hour interrogation, Frazier admitted he had cooperated with Salahuddin, a man he said he knew and feared.

Frazier also told police that Salahuddin had given him a phone number to be called if complications arose with transfer of the jeep. The number belongs to the Iranian Interests Section of the Algerian Embassy -- the only diplomatic representation of the Khomeini regime in Washington since formal diplomatic relations between the United States and Iran were severed in April.

One Algerian Embassy official said yesterday that Salahuddin is listed as an employe of the embassy, but did not specify in what division. Another embassy official who declined to be identified said the Iranian Interests Section is run by Iranians and only loosely associated with the rest of the embassy.

Before the diplomatic break, Salahuddin worked as a security guard at the Iranian embassy, according to Bahram Nahidian, a Khomeini supporter who is viewed by fellow Iranians as an unofficial spokesman for the regime.

(Ayatollah Mohammed Beheshti, chief justice of Iran's Supreme Court, said yesterday that Moslem law allows for "the formation of an Islamic group to destroy the leaders of blasphemy," according to Tehran radio monitored by the Associated Press. Beheshti, whose remarks followed the slaying of Tabatabai and an attempt on the life of a former Iranian official in Paris last Friday, said such a plan first would have to be "studied in detail" by Islamic leaders.)

Police and the FBI said there was no evidence that any foreign nationals were involved in the Tabatabai slaying.

Salahuddin has lived off-and-on at the Islamic House at 5714 16th st. NW, a gathering spot for Islamic students of all nationalities. The house, which is run by Nahidian, was searched yesterday by FBI agents, who left empty-handed.

Salahuddin and Nahidian were among seven persons arrested in New York City after briefly taking over the Statue of Liberty in an anti-shah rally Nov. 4 -- the day that American hostages were seized in Tehran.

The FBI and Montgomery County police obtained arrest warrants yesterday for:

Salahuddin, whose last known address was the Islamic House. Salahuddin, still at large, was charged with a federal civil rights violation and a state charge of murder.

Frazier, 31, who gave an address on Southern Avenue in the District. The postman is held without bond, pending arraignment today in Rockville, on a state charge of being an accessory before the fact to commit murder.

Horace Anthony Butler, 35, who gave an address of 4921 LaSalle Rd., Avondale, the residence of one of his brothers. Butler, arrested in his car yesterday by the FBI, is charged with a federal civil rights violation.

At Butler's arraignment yesterday at the Federal Courthouse in the District, Assistant U.S. Attorney E. Lawwrence Barcella Jr. argued successfully to U.S. Magistrate Arthur Bennett that Bulter should be held without bond.

"We're talking about a politically motivated murder arising out of Iran," Barcella said.

Also being sought is an unnamed suspect whose role included driving Salahuddin to the rendezvous with the jeep, according to the police. Postman Frazier said Salahuddin arrived as a passenger in a small blue 1974 or 1975 automobile driven by someone he believed to be a black male.

The fourth man, according to police, also may have driven a getaway car after the killer abandoned Frazier's jeep two blocks from the scene of the assassination.

Tabatabai, according to police was killed by three shots from a 9mm pistol allegedly fired by Salahuddin, who was dressed as a postal worker and went to the door saying he had two special delivery packages for Tabatabai.

When Tabatabai, a vehement critic of the Khomeini regime in Iran, came to the door and leaned down to inspect the packages, the gunman fired his weapon, which had been concealed behind two manila envelopes, police said.

Tabatabai died 45 minutes later at Suburban Hospital. Within hours of the shooting, police discovered Frazier's Postal Service jeep abandoned two blocks from the site. At 4 p.m. Frazier called his supervisors with his story that he had been abducted and his jeep had been hijacked.

By 2:46 yesterday morning, Frazier had changed his account, police said, and had given them a signed statement.

According to the FBI court statement, Frazier told investigators he had met Salahuddin at the home of a mutual friend last fall and, during a dozen meetings in the ensuing months, had come to know and fear Salahuddin as a man who "was involved with weapons and the martial arts and could hurt people."

So, last Sunday night, when Salahuddin asked to meet Frazier and, on meeting him, asked if he could borrow his jeep for a few hours for a $200 downpayment and $300 later. Frazier told police he agreed.

Yesterday, Montgomery police declined to say whether Frazier knew his jeep would be used as part of an assassination plot.

Frazier told police that he and Salahuddin met on Idaho Avenue NW, along Frazier's regular mail route, between 11 a.m. and 11:30 a.m. Tuesday.

Frazier said he turned over the jeep to Salahuddin, who was wearing a Postal Service uniform, and got in a blue 1974 or 1975 pickup truck driven by Butler. The fourth man apparently drove off in the blue car.

Butler and Frazier then drove to Baltimore and back in the pickup truck, spending more than five hours on the road before Frazier got out of the truck near a dairy store in Wheaton.

From there, Frazier told police, he walked to Sligo Junior High School, called his postal supervisor and reported his prearranged story about being kidnaped and held hostage at gunpoint.

Police said both Salahuddin and Butler were among the 400 persons photographed by the District police intelligence division during a months-long surveillance of the activities of an unnamed Muslim sect composed mainly of blacks.

These were the photographs which were shown to witness Mortazavi, an Iranian student working for his PhD. in anthropology at Temple University in Philadelphia.

Mortazavi told police he was visiting Tabatabai's home at 9313 Friar's Rd. in a wealthy section of Bethesda when the doorbell rang at about 11:45 Tuesday morning.

A man dressed as a postman told Mortazavi through the door that he had two special delivery packages for which receipts had to be signed. Mortazavi opened the door and started to sign for the parcels when the postman said, "No, Mr. Tabatabai has to sign for them." Mortazavi said the man was holding two envelopes in his left hand and had his right hand underneath the envelopes.

Tabatabai, who often had expressed fear for his life because of his outspoken views, heard the conversation and came to the front door, asking Mortazavi in Persian what was going on.

When Mortazavi told Tabatabai that the postman said the packages had to be signed for by him, Tabatabai came to the foyer, and bent over to look at the packages.

As he did, Mortazavi said he heard "two or three loud shots" and watched as Tabatabai fell on his back into the house.

Mortazavi slammed the door, glanced at the bleeding Tabatabai, and ran to the kitchen, calling to the two other occupants of the house. Them he telephoned for an ambulance.

The first arrest in the case was Frazier, charged after his interrogation had been completed.

Butler, the man with whom he drove to Baltimore, was arrested at about 1:30 p.m. yesterday in his car at Georgia Avenue and Jefferson Street NW by the FBI.

A county police source said that, shortly before his arrest, Butler was observed dropping off a package at the Islamic House on 16th Street in Northwest Washington.

During their five hours of driving, Butler described himself as a self-employed carpenter and handed Frazier an envelope with his name on it, saying Frazier should contact him if he ever needed any work done. Butler also told Frazier he was a Vietnam veteran.

There was no evidence, police said, that Butler and Frazier were members of any Muslim group.

Salahuddin -- who took the name of one of the greatest Muslim warriors -- is one of many American blacks who have joined pro-Khomeini fundamentalist Muslim groups in Washington.

The Muslims associated with these groups are not necessarily followers of the group once known as Black Muslims, a group founded by the late Elijah Muhammad which is now called the World Community of Islam in the West.