WASHINGTON — President Trump is expected to overrule his top national security advisers and decline to certify the Iran nuclear agreement, according to people who have been briefed on the matter, a decision that would reopen a volatile political debate on Iran but is likely to leave in place the landmark deal negotiated by the Obama administration.

By declining to certify Iran’s compliance, Mr. Trump would essentially kick it to Congress to decide whether to reimpose punitive economic sanctions. Even among Republicans, there appears to be little appetite to do that, at least for now.

Still, Mr. Trump’s expected move would allow him to tell supporters that he had disavowed the accord, while bowing to the reality that the United States would isolate itself from its allies if it sabotaged a deal with which Iran is viewed as complying. Mr. Trump repeatedly ridiculed the accord during the 2016 presidential campaign, vowing to rip it up.

White House officials cautioned that the president had not yet formally decided to “decertify” the agreement. But he faces an Oct. 15 deadline, and he has made little secret of his intentions, most recently when he declared at the United Nations two weeks ago that the agreement was “embarrassing to the United States.”