JERUSALEM — Defense Secretary Chuck Hagel opened a weeklong visit to the Middle East on Sunday by pressing an American agenda focused on deterring Iran — including a significant new weapons deal for Israel — coupled with a strong caution that it would be premature for Israel to opt for unilateral strikes on Tehran’s nuclear program.

Mr. Hagel, who was subject to intense, even hostile scrutiny during his confirmation process over whether he was sufficiently supportive of Israel, hailed the “very special relationship” between the United States and Israel. He also repeatedly emphasized Israel’s right to defend itself “in a very dangerous, combustible region of the world.”

In preventing Iran from acquiring nuclear weapons, the United States has said that all options are on the table, including military action. But President Obama and his national security team have argued for more time to pursue diplomacy and economic sanctions. Some Israeli leaders, though, say the timeline for Iran to build a nuclear bomb is short, and they regularly speak of unilateral action.

In recent days, Israeli officials have again discussed their right to act against Iran. But American national security officials and military officers say it is unlikely that a strike by Israel would be sufficient to terminate Iran’s nuclear program or halt any ambitions by Tehran to obtain nuclear weapons. Iran has denied it seeks to build nuclear weapons and has said its enrichment program is for civilian use.