Alexander Learned Singer died for his adopted country this week. Those who knew him -- who watched him mature from a Chevy Chase schoolboy into a thoughtful young man of the world, and a soldier for Israel -- those friends had no trouble yesterday explaining his death.

"Alex had a cause, a conviction, something he believed in," one of them said of Singer, who emigrated to Israel in 1985 after months of soul-searching and died Tuesday night leading an army patrol in south Lebanon.

It was his 25th birthday.

A 1980 graduate of Bethesda-Chevy Chase High School, Singer formed a deep attachment to Israel while living there in the early 1970s, friends said. After graduating from Cornell University with honors, they said, he embarked on an intellectual journey across Europe and the Middle East, seeking his right place in the world.

"Where could he help? Where was the good fight?" said Barbara Ledeen, a family friend. "And I remember, when he was back home once, he said, 'Here, you're one of 200 million. But if you're in Israel, it's small, and the least little thing you do has an effect.' "

Capt. Singer, a platoon commander, was leading his men along the western slopes of Mount Hermon inside the Lebanese border when they came across a band of Palestinian guerrillas intent on penetrating Israeli territory, the Israeli army said. He was among three soldiers killed in the clash.

His parents, Max and Suzanne Singer of Chevy Chase, traveled to Jerusalem with relatives and friends to witness his burial yesterday in a military cemetery on Mount Herzl in Jerusalem. One brother, Daniel, is a paratrooper in the Israeli army.

Others who remained behind also mourned his death.

"Alex was brought up to see the importance of freedom," said David Bardin, another family friend. "And Israel to him, despite its warts, stood for freedom and enormous potential. And combine that with his optimism, which was basically American. That was Alex."

Ledeen said Singer discovered Israel early in his life, when his parents moved with their four children from New York to Jerusalem in 1973.

Max Singer, now a public policy analyst with the nonprofit Potomac Organization in Arlington, "wanted to get in touch with his roots," Ledeen said. He developed an abiding love for Israel and a deep appreciation of its importance as a Jewish homeland, and passed on those feelings to his sons.

The family resettled in Montgomery County in 1977. Alex Singer, having finished the ninth grade at a kibbutz school in Israel's southern desert area, enrolled as a sophomore at Bethesda-Chevy Chase High School.

As a senior, he signed up for James Biedron's Mideast history course.

"He was really a student," Biedron recalled. "He had intellectual curiosity. He could analyze things. He had an inquiring mind. He came away with a real understanding of things."

Although Singer believed strongly in the legitimacy of the Israeli state, Biedron said, he tolerated differing ideas -- even sought them out. When the class conducted a mock Middle East peace conference, he said, Singer chose to represent Syria.

"It was typical of him," Biedron said. "When he conversed with you, he was always interested in your point of view. He was aware that it was necessary to protect Israel, but he was aware of other perspectives."

After Cornell, he explored Europe and the Middle East, writing long, thoughtful letters to his parents, addressing them: "Dear Everyone . . . ' His mother or father typed each letter, made photocopies and passed them along to friends and relatives, or anyone interested in Alex.

These weren't just travelogues," said Shulamith Elster, headmaster of the Charles E. Smith Jewish Day School in Rockville and a family friend. "These were the observations of a young man in search of the people and places and experiences that together would help him understand the world. This wasn't just some kid out on a European junket."

Ledeen said Singer visited and talked for hours with Jewish families in several countries, including the Soviet Union. "He made it his business to meet them," she said. "He wanted to learn about their roots, where they had come from. And he reached a decision that these people weren't secure, that they didn't feel very secure in their communities. And he decided that it was a good thing there was an Israel."

He had always believed in Israel. Now he chose to become part of it.

"He found his place in God's world," Elster said.

Singer was drafted into the Israeli army and quickly decided to become a professional soldier, a paratrooper and officer in the elite Givati Brigade.

"Alex wanted to physically embody the ideas he had," said Ledeen. "He just didn't want to sit and talk about them. He wanted to do it."

And, Elster said, he wanted to teach others to open their minds, as he had.

"He wanted to help young people shape their lives, mold their lives, figure out what was important to them in life," Elster said. "I see him not so much as wanting to be a commander. He wanted to be mentor."