Lionel A. Rosenblatt, a U.S. Foreign Service officer, who helped roughly 200 South Vietnamese citizens evacuate Saigon days before it fell in 1975 with a daring, unauthorized mission that prefaced a career advocating for refugees in Southeast Asia and other global hot spots, died on April 11 at his home in Washington. He was 82.

Concerned about the fate of the Vietnamese who had worked with the United States during the war, tens of thousands of whom could be vulnerable to retribution by the Communist North Vietnamese government, Mr. Rosenblatt said, “Our lives depended on their ability to help us. To up and leave them was unthinkable.”

They phoned their network of former colleagues. They scheduled meet-ups on street corners, a restaurant, a cathedral, offering passage out of Vietnam, warning that it was a risky and dangerous mission. They shepherded their Vietnamese friends to military planes leaving for Guam and the Philippines and eventual travel to the United States. On April 30, Mr. Rosenblatt and his colleague, Larry Craig Johnstone, left the country in the last American helicopter to make a rooftop departure out of the country.