DHAHRAN, Saudi Arabia (AP) _ FBI Director Louis Freeh began a visit to Saudi Arabia Wednesday to check on the investigation into the deadly bomb attack on a U.S. base.

The June 25 blast killed 19 American servicemen and injured hundreds at the U.S. military housing complex in Dhahran, in eastern Saudi Arabia. It was the worst terrorist attack on U.S. forces in the Persian Gulf.

Muslim militants who oppose the presence of Western military forces in the kingdom are suspected of being behind the blast. Saudi Arabia is home to Islam's holiest shrines.

An FBI statement said Freeh will meet Saudi leaders and visit the bombing site in Al-Khobar, a Dhahran suburb. The attackers are believed to have driven a bomb-laden fuel truck up to the compound and detonated it.

More than 40 FBI agents, including an explosives unit, an evidence team and anti-terrorism squads were sent to Dhahran immediately after the blast to help Saudi investigators. More agents were dispatched Sunday.

The FBI team has refused to speak with reporters and details of Freeh's engagements in Saudi Arabia were not released.

U.S. officials have said the investigators have several clues, including the chassis of the truck, the chassis' serial number, and a crankshaft.

Gulf newspapers say Saudi officials also have the truck's license plate number and plan to release sketches of two suspects.

In Washington, a U.S. State Department spokesman said the investigation is being carried out in Saudi Arabia and elsewhere, but added that there has been no hint that other countries played a role in the attack.

``We have no indication that would lead us to believe at the present time that any (non-Saudi) state was involved in this,'' said Nicholas Burns.

The United States posted a $2 million reward Tuesday for information leading to the arrest of the bombers. Saudi Arabia has offered $2.7 million.

Also Wednesday, a doctor and three security police received one of the U.S. Air Force's highest non-combat medals for bravery in response to the bombing.

Gen. Ronald R. Fogleman, the Air Force chief of staff, flew in from Washington to honor the survivors of the bomb attack.

The honored security police had been standing guard on a building roof and risked their lives trying to evacuate it after seeing the suspicious truck. They were running down hallways knocking on doors when the bomb went off.

They are Staff Sgt. Alfredo R. Guerrero of Modesto, Calif., Airman 1st Class Christopher Wagar of Graham, Wash., and Senior Airman Corey P. Grice of Lattia, S.C.

The doctor _ Maj. Steven Goff of Big Bend, Wis. _ treated scores of injured troops although he had himself suffered a chest wound.

About 100 Air Force troops, with crutches, neck braces or bandages, attended the awards ceremony in the housing compound's cafeteria.

``I applaud the magnificent way you responded to that terrorist attack,'' Fogleman told the group.

``There were many heroes'' that night, and ``extraordinary actions became ordinary feats,'' he said.

Fogleman cast no blame, but echoed Clinton's message: ``Our nation will not back away from our commitment here.''

Air Force troops based in Dhahran fly observation missions over southern Iraq to enforce U.N. sanctions. They are among 5,000 American military personnel stationed in the kingdom to keep an eye on Iraq since its eviction from Kuwait in the 1991 Gulf War.