OFRA, West Bank — YEHUDA ETZION does not regret, exactly, helping plant bombs in the cars of Palestinian mayors and plotting to blow up the Dome of the Rock in the 1980s, nor does he express remorse. But he has reconsidered the role of violence in the quest for a Messianic kingdom of Israel, particularly as he contemplates a new generation of radicals he sees as bastardizing their shared ideology.

Yes, the aging right-wing extremist is wringing his weathered hands along with much of the Jewish world after last month’s firebombing in the West Bank village of Duma that killed an 18-month-old boy and his father. It is personal for Mr. Etzion, 64, who said he takes “partial responsibility” for not reaching out to the young zealots “to try and straighten out their thinking,” which he described as a “superficial,” “childish,” “distorted” and even “vulgar” interpretation of Jewish texts.

Having spent the decades since he was released from prison in 1989 mostly writing and editing books — while continuing to promote a vision of a third Jewish temple where the sacred Islamic dome now stands — this icon of the Jewish Underground issued a one-page declaration, gave a lengthy interview to a conservative newspaper and went on television to condemn the Duma arson. Mr. Etzion said if he knew the perpetrators, he would turn them in to the police, prompting a backlash from some longtime friends.

“I can hardly find words strong enough to say how I distance myself from them and reject them,” Mr. Etzion said in a conversation at his home in Ofra, the West Bank settlement he helped found 40 years ago.