President Trump said Monday that he had authorized a new wave of strikes against Iran this week but that he was holding off to make room for “serious negotiations,” after he said three Gulf leaders requested more time to work out a nuclear deal. Mr. Trump has repeatedly threatened to launch new strikes, only to pull back at the last minute from plunging the United States back into an unpopular, expensive war. “We were getting ready to do a very major attack tomorrow, and I put it off for a little while, hopefully maybe forever, but possibly for a little while,” Mr. Trump told reporters. When Mr. Trump launched the war alongside Israel on Feb. 28, he estimated that it would end in four to five weeks. The conflict is now in its third month, and Mr. Trump is caught between dueling impulses: to force Iran into submission, and to declare victory and move on. U.S. military officials say that the Iranian regime has demonstrated enormous resilience. Still, the military campaign has hit Iran hard: the Pentagon estimates it has destroyed some 13,000 targets. The war remains deeply unpopular at home. Mr. Trump did not specify what targets the United States had planned to strike on Tuesday, but officials said the military had developed a variety of options, including targeting the country’s ballistic missile sites.