A Middle East man who authorities believe could implicate a suspected Lebanese terrorist in the 1985 hijacking of a Jordanian airliner was jailed here Friday as a material witness, according to court records and sources.

Mouin Abdul Ajam was arrested in California on Thursday and flown to Washington, D.C., following a hearing before a federal magistrate in Sacramento, according to court records in that city.Ajam was named in an arrest warrant outlining Justice Department concerns that he might not cooperate in the prosecution of hijacking suspect Fawaz Younis, said Jessica McGuire, an assistant federal public defender who represented Ajam in Sacramento.

Younis, a former member of Lebanon's Shiite Amal militia, is awaiting trial here on hijacking charges.

Federal prosecutors have also filed a motion to compel Ajam to give a sworn deposition about the case, said sources familiar with the case who spoke on condition of anonymity.

Justice Department spokesman John Russell declined to comment.

Younis, who was arrested last September after he was lured aboard an FBI-chartered yacht in the Mediterranean, is charged with leading the June 11, 1985, hijacking of a Royal Jordanian airliner in Beirut.

Federal prosecutors have jurisdiction to prosecute the case because the plane was carrying several Americans. No date has been set for Younis' trial in U.S. District Court.

McGuire said Ajam is "extremely concerned" that if he cooperates with the prosecutors in the case, his family in Beirut will be killed in retaliation by terrorist groups sympathetic to Younis.

"He has every reason to fear retaliation against his family in Beirut," she said. Ajam complained that the U.S. government is "not taking enough precautions regarding his family," she said.

Prosecutors disclosed in court last month that two airline crew members are in protective custody after agreeing to come to this country and testify against Younis.

The FBI was trying to locate a Middle Eastern passenger whohad once identified Younis at a lineup.