Since leaving office in 2008, Mr. Olmert has often urged caution concerning Iran. His remarks on Sunday were noteworthy for their place and time — before an audience of some of Mr. Netanyahu’s strongest American supporters, and only a few days after Israel’s top military officer suggested that the threat posed by Iran was less urgent than Mr. Netanyahu has said, and the former head of Israel’s internal security service said the prime minister had “messianic feelings.”

Illustrating how visceral the debate has become, and how entwined it is with politics in both Israel and the United States, some in the crowd peppered Mr. Olmert with shouts of “Naïve!” and “Neville Chamberlain!” and booed loudly when he called for a less confrontational stance toward President Obama, whose political opponents Mr. Netanyahu has openly courted.

“You have to respect him,” Mr. Olmert said of Mr. Obama. “He is the president of the most powerful nation on earth, and happens to be a friend of Israel.” When boos rang through the conference room in response, he joked, “I can see that this hall is full of Democrats.”

Mr. Olmert was booed again when he declared that while Israel should prepare the military ability to strike Iran’s nuclear program as a last resort, it should first push for American-led international action against Iran, including sanctions and possible joint military action.

This time, he responded caustically.

“As a concerned Israeli citizen who lives in the state of Israel with his family and all of his children and grandchildren,” he said, “I love very much the courage of those who live 10,000 miles away from the state of Israel and are ready that we will make every possible mistake that will cost lives of Israelis.”