A Saudi man being held on suspicion of involvement in the 1996 bombing of a U.S. military housing complex in Saudi Arabia will be deported to that country later this week unless he cooperates with American investigators by Wednesday, administration officials said last night.

Hani Abdel Rahim Sayegh was arrested in Canada after the bombing and has been held in the United States since June 1997. U.S. law enforcement officials believe Sayegh may have information pointing to Iranian involvement in the attack, which killed 19 American service personnel and wounded more than 500 others at the Khobar Towers housing complex in the eastern Saudi city of Dhahran.

Sayegh initially agreed to cooperate with the Justice Department in a separate terrorism case, but he reneged on the deal and the department began proceedings to have him returned to Saudi Arabia. Officials expressed hope last night that Sayegh would change his mind and agree to cooperate in the probe rather than return to Saudi Arabia, where he faces trial and execution by beheading if convicted.

But the Justice Department's willingness to surrender its star--indeed its only--witness in the Khobar case to Saudi authorities shows the frustration of U.S. law enforcement officials after three years of inconclusive digging. With the case at a virtual standstill, President Clinton in August took the extraordinary step of appealing directly for help to Iranian President Mohammed Khatemi, a moderate cleric who has called for better relations between Iran and the West.

But Khatemi's government denied any involvement in the Khobar attack in an official response to Clinton's message several weeks ago, U.S. officials said. The Iranian reply noted also that the United States did not prosecute the captain of the USS Vincennes, the warship that downed an Iranian passenger jet in 1988, killing 290 people.

Justice Department officials informed Sayegh last week that he would have until Wednesday to cooperate in the probe or be removed to Saudi Arabia, sources familiar with the matter said. One of Sayegh's attorneys indicated he may seek to delay his removal from the United States by filing a motion in court.

While Sayegh is suspected of involvement in the Khobar Towers bombing, the United States does not have evidence that would stand up in an American court, officials said. However, the Saudi Arabian government has informed U.S. officials that "it has a basis" for prosecuting him, according to the Justice Department.

The Saudi government has provided assurances that Sayegh will not be tortured if he is returned to that country, officials said.

The Justice Department said yesterday for the first time that Iranian government officials are under investigation in connection with the attack.

"The U.S. investigation of the attack at Khobar is ongoing," said Deputy Attorney General Eric H. Holder Jr. "We are investigating information concerning the involvement of Saudi nationals, Iranian government officials and others. And we have not reached a conclusion regarding whether the attack was directed by the government of Iran."

The United States does not have an extradition treaty with Saudi Arabia. The Saudi government has other individuals under detention pending trial in the Khobar case, but it did not request that Sayegh be sent home. However, the Justice Department's decision increases the pressure on him to cooperate in the probe.

Attorney General Janet Reno authorized Sayegh's removal last week and notified his lawyers of the decision after consulting with the secretary of state and other senior administration officials, Holder said. Sayegh has been in removal proceedings since 1997 and sought immigration relief under the Convention Against Torture. But last week, Justice officials concluded that he was not entitled to remain in the United States.

Clinton's request to Iran was based in part on intelligence reports linking the bombing to three Saudi men who have taken refuge in Iran, a senior official said. The three men are thought to be affiliated with a Shiite Muslim extremist group known as Saudi Hezbollah. Shiite Muslims constitute a minority in Saudi Arabia, which is predominantly Sunni Muslim, and many Shiites feel at least a spiritual kinship with the Shiite clerics who rule Iran. Sayegh also is Shiite Muslim.

Shortly after he was deported from Canada to the United States, Sayegh identified Brig. Ahmad Sherifi, a senior Iranian intelligence officer, as a key figure in a 1995 plot that never resulted in an attack but is believed by some U.S. officials to have evolved into the Khobar bombing, sources told The Washington Post in 1997.