A White House spokesman, Roman Popadiuk, said, "We hold the kidnappers responsible for his safety."

Higgins had been on U.N. duty in the Middle East since June 1987 and assumed command of the Lebanon observer group in mid-January, said U.N. officials in New York.

A Pentagon official, speaking on condition of anonymity, said 15 or 16 Americans were assigned to the observer group, but the U.N. put the number at 17. Goksel said only six were actually in Lebanon.

Officials said it was not unusual for several members of the observer group to be out of the country at a given time.

The Pentagon said Higgins joined the Marine Corps in 1967 and saw combat in Vietnam. He has received numerous military decorations, including the Defense Superior Service Medal, the Bronze Star with Combat "V," the Meritorious Service Medal and two Navy Commendation Medals.

He is married to Marine Maj. Robin Higgins, who works at the Pentagon. She declined comment. He has a 17-year-old daughter by a previous marriage.

An uncle, Delbert Eagle, 86, of Lancaster, Ky., said Higgins' lifelong ambition was to be in the military.

"Yes, he wanted to be in the military service. He always talked about wanting to go to the military service," Eagle said. He added that Higgins' mother died several years ago and his father is in a Louisville hospital.