After the barracks bombing, Reagan had a choice: Commit more forces to Lebanon only nine years after Vietnam, when public support for a long military conflict was low, or retreat.

"It's a hard thing to say, it's a hard thing to accept, but we had lost," said Ryan Crocker, the political officer in the Beirut embassy, who later became Deputy Secretary of State for Near East Affairs. "The situation would not have gotten any better. We would have had more dead Marines."

To political and military leaders in the United States, the pullout made sense. With a crippled Marine battalion and no clear military target, some thought withdrawal was the only option.

"You can't police the world," said P.X. Kelley, the then-Marine commandant. "Sometimes the best option is to do nothing."

But to terrorists and their backers, it was a sign of weakness, confirming their belief that the Americans had no staying power. The Syrian prime minister had told Morris Draper, a special presidential emissary, just months before: "You Americans can't hold your breath."

The U.S. response to the barracks bombing was limited. Despite indications that it was carried out by the radical Islamic group Hezbollah and backed by Iran, a planned U.S. military mission to bomb terrorist training camps was never carried out.

Top Reagan officials disagree on why. Weinberger says a conclusive link to Iran and Hezbollah was never proven. McFarlane said Weinberger was too concerned about the political risks of failure and losing support from U.S. allies in the Arab states.

Either way, critics say the lack of retaliation cemented America's weak image in the Arab world.

"If we had struck back and pulled out," said Bill Cowan, part of a top secret intelligence team sent to investigate the bombings, "we wouldn't have been leaving with our tail between our legs."

Two decades of Arab-backed terrorism have followed the bombings of the Marine barracks and the U.S. Embassy in Beirut.

American soldiers are "paper tigers," Osama bin Laden told ABC News in 1998. "The Marines fled after two explosions."

Using the Beirut bombings as a guide, terrorists:

—attacked American embassies in Kuwait two months later, and Kenya and Tanzania in 1998, killing 307 Americans and others.

—hijacked TWA Flight 847 for 17 days in 1985, taking hostages and killing a Navy diver.

—exploded Pan Am Flight 103 over Lockerbie, Scotland, in 1988, killing 270.

—bombed the World Trade Center in 1993, killing six and wounding about 1,000.

—killed 19 Americans in the 1996 bombing of Khobar Towers, a U.S. military base in Saudi Arabia. The attack also wounded more than 370 Americans and Saudis.

—struck the USS Cole in Yemen in 2000, killing 17 sailors and injuring 39 others.