Senator Tim Kaine, Democrat of Virginia, is leading a push to curb President Trump’s authority to use U.S. forces to engage in hostilities against Iran, as the war between Israel and Iran raises fears of American entanglement in a broader conflict.

A resolution Mr. Kaine introduced Monday would require explicit congressional authorization or a formal declaration of war before U.S. forces could take direct action against Iran. It faces long odds on Capitol Hill given Republicans’ reluctance to challenge Mr. Trump’s power, but it could prompt a vibrant debate as lawmakers in both parties warn against involving the United States in the escalating conflict.

The measure is a direct invocation of the War Powers Resolution, a 1973 federal law intended to be a check on the president’s power to enter an armed conflict without the consent of Congress. While it would still allow Mr. Trump to authorize military action in self-defense in the event of an imminent attack, it would compel him to seek approval before carrying out any offensive operations against Iran.

“It is not in our national security interest to get into a war with Iran unless that war is absolutely necessary to defend the United States,” Mr. Kaine said in a statement announcing the resolution. “I am deeply concerned that the recent escalation of hostilities between Israel and Iran could quickly pull the United States into another endless conflict.”

Since Mr. Trump returned to office in January, Mr. Kaine has led a number of efforts to reassert congressional authority and reclaim power from the executive branch, whether by challenging presidential power over tariffs or scrutinizing U.S. military support for countries with troubling human rights records.

His latest effort reflects growing concern among some on Capitol Hill about the risk of being dragged into a regional war without public debate or legislative approval, though some lawmakers have expressed a willingness to lend additional military support to Israel if tensions with Iran continue to escalate.