The Federal Bureau of Investigation took the unusual action yesterday of offering a $10,000 reward from its own budget for information about the whereabouts of the District man charged in the assassination of Ali Tabatabai, the outspoken Iranian exile who was gunned down at his Bethesda home on Tuesday.

In announcing the reward -- the first of its kind offered since an FBI agent was killed in an ambush in Cleveland last summer -- the FBI said it believes the suspect, Daoud Salahuddin, also known as David Belfield, "is still in this area."

Salahuddin, 29, is a member of a Muslim sect and worked as a security guard at the Iranian Embassy here after the fall of Shah Mohammad Reza Pahlavi. More recently, he was reportedly employed at the Iranian Interests Section in the Algerian Embassy, the Washington base for the regime of Ayatollah Ruhollah Khomeini.

Although the search for Salahuddin was concentrated in the Washington area, more than 100 law enforcement officers, including FBI agents from Baltimore, Silver Spring and Washington and police from Montgomery County and the District, were tracking down leads that suggested Salahuddin, a one-time house painter and handyman, might be across the country, or even abroad.

Tabatabai, 49, who served as a press attache at the embassy here under the shah, will be buried today in the Islamic Garden in Falls Church, after a funeral service at the Islamic Center, 2551 Massachusetts Ave. N.W.

Police said they have given protection to another former Iranian diplomat after he reported receiving threats on his life following Tabatabai's murder.

One of the two men already arrested and charged in connection with Tabatabai's death, Washington postman Tyrone A. Frazier, was denied release on bond during a 15-minute arraingment yesterday in ockville.

Frazier is accused of renting his government-owned jeep to Salahuddin. A witness to the killing said a man dressed in a postal uniform gained entrance to Tabatabai's house at 9313 Friars Road, Bethesda, by saying he had two special delivery packages that had to be signed for by Tabatabai. Frazier identified Salahuddin as the man to whom he gave his jeep, in return for $200 down and a promise of $300 more later.

At yesterday's arraignment, Frazier told District Court Judge Charles W. Woodward Jr., "I had no knowledge of any murder that was to be committed."

Judge Woodward ordered Frazier held without bond despite protestations from Frazier's lawyer, former D.C. Superior Court Judge Harry T. Alexander, who was been representing the 31-year-old letter carrier in a divorce action.

Alexander complained that Frazier had been denied the services of a lawyer during the 10 hours in which the mailman was questioned by Montgomery police and the FBI.

Frazier originally contended that he had turned over his jeep at gunpoint, and was then held hostage for more than five hours by "two white men" who drove him around the area. Later, however, Frazier changed his story and said the he had agreed to rent his postal jeep to Salahuddin for $500.

"He asked for a lawyer on many occasions" during the long interrogation, Alexander told the judge. The Defense attorney described his client as "an innocent victim. He had no knowledge of any plan, conspiracy or murder of Mr. Tabatabai."

Alexander said that "if there's any (complicity), it's only with respect to loaning the jeep."

Assistant State's Attorney Anne Harrington told the judge that the crime with which Frazier is charged -- accessory before the fact of first degree murder -- carries a maximum penalty of life in prison and that "the evidence is very strong."

The prosecutor said "the court should consider the deceased's identity" when deciding whether to set bond.

She added that Frazier had been shuttling between his parents' home on Southern Avenue and a girlfriend's house on Alabama Avenue in the District.

Frazier, dressed in the tan fatigues of the Montgomery County Detention Center, appeared calm throughout the short hearing, at one point waving discreetly to his parents, who came to the court with one of Frazier's brothers.

A third person charged in the killing, Horace Anthony Butler, 35, was arrained in U.S. District Court in Washington on Wednesday, and he, too, was ordered held without bond at the D.C. jail.

A fourth unnamed suspect, who may have driven the getaway car, also is being sought.

The international implications of the shooting prompted a high-level meeting at the Justice Department on Wednesday, where arrangements were made for the Central Intelligence Agency to cooperate in the probe.

The CIA is prohibited by its charter from participation in U.S. criminal investigation, but the agency provided extensive information from foreign sources following in the assassination of former Chilean ambassador Orlando Letelier here in 1976.

Meanwhile, wary District police are weighing requests by two more Iranian groups -- making a total of four -- who want to demonstrate here sunday.

The Iran Freedom Foundation, the anti-Khomeini group founded by Tabatabai, will go ahead with a march and rally -- originally planned by Tabatabai -- as a tribute to its slain leader.

Before the killing, the leftist Iranian Student Association, had also obtained a permit to march Sunday along a route bounded by 14th, I, 18th and E streets NW, a block removed from the IFF rally.

Yesterday, the Confederation of Iranian Students, also a leftist group, sought permission to march along the sidewalk parallel to the procession of the IFF, from the U.S. Capitol to Lafayette Square.

And the Moslem Student Association, another pro-Khomeini organization, applied for a permit to hold a rally in Lafayette Square in the morning, promising to vacate the park across the street from the White House, and move on to Dupont Circle when the IFF for its scheduled 2 p.m. rally.