Federal officials are searching for a D.C. man whom they want to question in their investigation into the assassination of Iranian exile leader Ali Akbar Tabatabai, who was shot to death on the doorsteps of his Bethesda home last July.

John Leo Roberts, also known as Yahya Kwasi Jalal, has been declared missing since Monday afternoon after he failed to show up at the U.S. District Courthouse here to surrender to federal agents on charges of illegally purchasing a handgun.

Yesterday, officials announced the posting of a $1,000 reward for information leading to Roberts' arrest. They said they believe he had left the Washington area and might be making plans to leave the country. Roberts, 37, who was living at 4018 Illinois Ave. NW, should be considered "armed and extremely dangerous," an FBI spokesman said.

Roberts' lawyer, Richard C. Deering, said yesterday, "I have no reason to believe he has fled."

Deering confirmed that Roberts is a friend of Tabatabai's accused assassin, Daoud Salahuddin, also known as David Belfield, and that the two worked together as security men at the Iranian Interest Section of the Algerian Embassy in Washington until they were fired shortly after the slaying.

But, Deering said, Roberts had "absolutely no connection" with the Tabatabai murder. "He was very shocked that [federal officials] even suspect [Salahuddin]," the lawyer said. "He knew Daoud as a very peaceful fellow."

Federal officials investigating the Tabatabai slaying have focused their attention on Salahuddin, who is charged with the murder, and other members of a small group of militant black American Muslims who have adopted the revolutionary version of Islam advocated by Iranian leader Ayatollah Ruhollah Khomeini. Authorities have described the murder of Tabatabai, press attache at the Iranian Embassy under the late, deposed shah, as a carefully plotted attempt to silence a leading critic of the Khomeini regime.

Salahuddin, who investigators said fled the country within 24 hours after the slaying, is now believed to be living in Iran. Another man federal officials have linked to the murder plot, Musa Abdul Majid, is also believed to have fled the country after he was convicted of charges of illegally buying five hand-guns and one box of 9 mm. shells.

In January, after Majid failed to appear for sentencing on the firearms charges in federal court in Alexandria, prosecutors said he is believed to have furnished the ammunition -- and perhaps the weapon -- used to murder Tabatabai.

Tabatabai was shot July 22 when he accepted delivery of two packages, purportedly from Salahuddin, who was said to be dressed in the uniform of a postal carrier, investigators said.

Roberts' lawyer Deering, said his client was last seen leaving his home shortly before 5 p.m. Monday. In a telephone conversation at 4:25 p.m. that day, Deering said Roberts told him he was on his way to the courthouse.