EMANUEL GROSS, a professor of law at the University of Haifa and a former military judge, said it would be “dangerous” to accept the right of people like Mr. Blanc not to serve in the army.

“Today you may be accepting a person with one ideological viewpoint and tomorrow you might have another person with another ideological viewpoint,” Mr. Gross said, adding, “There is no place in the army to raise political views.” He said that while he understood those who resist the idea of Israel’s staying in the occupied territories, the army would have sent a clearer message by court-martialing Mr. Blanc to a longer jail term.

Mr. Blanc’s route to conscientious objector started when he was a schoolboy. He grew up in a left-leaning household and attended demonstrations and Israeli-Palestinian coexistence activities with his parents. But his first real awareness, he said, occurred while he was in high school and became upset by what he called a systematic attempt to “brainwash” the students.

He recalled a trip to the Golan Heights, the strategic plateau that Israel seized from Syria in the 1967 war. On the high ground overlooking northern Israel, the pupils met Avigdor Kahalani, a retired general who commanded a decisive battle there in 1973. “He tells his story, points to the hills and says: ‘I think the Syrians are watching us now. Can I count on you?’ Everybody shouts, ‘Yes!’ ” Mr. Blanc recounted. “It was a very traumatic experience for me.”

Mr. Blanc’s grandfather was an officer in the United States military who came to fight in Israel’s war of independence in 1948 and was wounded. Both his parents served in Israel’s military intelligence. One sister served in military intelligence, and another was exempted as a pacifist. “We have very different opinions,” he said of his family.

Mr. Blanc said he first began considering refusal in the winter of 2008-9, when Israel carried out a devastating military offensive in Gaza aimed at stopping Palestinian militant rocket fire against southern Israel. At first his parents opposed his refusal and hoped that he would change his mind, he said, but later they came to see his view as legitimate, even if they disagreed with it.

He said the argument that it is better to try to influence the army’s conduct from within was “acceptable, but you have to draw the line.”