WASHINGTON – Iran must pay $2.65 billion to the families of the 241 American service members killed in the 1983 bombing of the American Marine barracks in Beirut, a federal judge declared yesterday in a ruling that left survivors and families shedding tears of joy.

Federal District Judge Royce C. Lamberth described his ruling as the largest-ever such judgment by an American court against another country. “These individuals, whose hearts and souls were forever broken, waited patiently for nearly a quarter century for justice to be done,” he said.

Iran has been blamed for supporting the militant group Hezbollah, which carried out the suicide bombing in Beirut. It was the worst terrorist act against American targets until the September 11, 2001 attacks.

Hundreds of people crowded into a federal courtroom to hear yesterday’s ruling. Parents have grown old since their children were killed. Siblings have grown into middle-age. Children have married and started families of their own.

Weeping spectators stood and erupted in applause and hugs as Judge Lamberth left the bench.

The ruling allows nearly 1,000 family members and a handful of survivors to try to collect Iranian assets from various sources around the world. Finding and seizing that money will be difficult, however, and the families are backing a law in Congress that would make it easier for terrorism victims and their families to do so.

Families were encouraged by Libya’s decision to ultimately accept responsibility for the 1988 bombing of a Pan Am flight over Scotland. The country, once a pariah by Washington’s view, agreed to compensate the families of the 270 victims. Part of the $2.7 billion has been paid. A final $2 million installment to each family is outstanding.

“This is a sense of victory, of winning a battle,” said Paul Rivers, who was a 20-year-old enlisted Marine on the second floor of the barracks when it exploded. “When we win the war is when we collect, when we make them pay for what they did.”

Iran has denied responsibility for the attack. The nation did not respond to the 6-year-old lawsuit and was represented only by an empty table.

Family members said they hoped Friday’s ruling would pressure foreign governments not to sponsor terrorism. Lynn Smith Derbyshire, whose brother, Vincent Smith, was killed in the attack, said countries won’t stop until “it begins to actually cost them money to kill Americans.”

Some disagreed about whether that will happen. Roxanne Garcia-Bates, who was 16 when her brother, Randy Garcia, was killed, said she was surprised to find a sense of comfort being with the other families in court. She said she was pleased that Lamberth had made such a strong statement, but doubted that Iran would change anytime soon.

“You can’t take enough money away to get them to stop what they’re doing,” she said.

All agreed that emotions remain raw to this day.

Mr. Rivers described being one of the second floor’s five survivors. All but him lost arms or legs, he said. He was buried in the rubble for two hours, he said. Debris had punctured his eardrum and “I literally had rocks inside my head.”

Shirley Murry of Baltimore, who was 16 years old at the time, described the tense days of waiting around the television for word of her brother, Ulysses Parker. Today, every time the news carries a story about a fallen soldier or an explosion overseas, she said it’s like that first day all over again.

Judge Lamberth said the law “offers a meager attempt to make the surviving members whole.” He said he hoped the judgment would alert Iran that terrorism has consequences and help in the families’ healing process. Pausing, he added:

“That’s all I can do.”