“This administration has largely failed to fulfill this legal obligation,” the lawmakers continued, mentioning the January drone strike that killed General Suleimani.

The letter was signed by the Democratic members of the so-called Gang of Eight, who are regularly briefed by intelligence agencies on sensitive national security developments: Speaker Nancy Pelosi; Representative Adam B. Schiff of California, the chairman of the House Intelligence Committee; Senator Chuck Schumer of New York, the minority leader; and Senator Mark Warner of Virginia, the top Democrat on the Senate Intelligence Committee.

The letter cited media reports about the administration’s consideration of direct action against Iran in response to attacks on American forces in Iraq by Iranian-sponsored militias. It was sent on the same day that The New York Times reported that the Pentagon was planning for a potential escalation in operations against Iranian militias.

Secretary of State Mike Pompeo and other officials have privately pushed for more direct attacks on Iranian forces, as part of an effort to force Tehran to the bargaining table.

Mr. Trump had resisted Mr. Pompeo’s proposal for tougher action, noting in the deliberations with his national security team that with Iran reeling from the coronavirus, a direct attack would appear inappropriate.

But Mr. Pompeo and some other senior administration officials have become frustrated with the violence in Iraq and near-daily American intelligence reports that Iran’s proxy forces are plotting against the United States. Mr. Pompeo, along with Robert C. O’Brien, the national security adviser, and Richard Grenell, the acting director of national intelligence, have argued that bolder action against Iranian forces could break the current cycle of violence and give new life to efforts to restart negotiations with Tehran.

Administration officials have maintained for nearly a year that a harsh approach toward Iran, including a campaign of financial warfare, would hurt Iran’s economy to the point of forcing its government to negotiate over its nuclear program and its military operations throughout the Middle East. Instead, Iran has lashed out with attacks for months against American forces and allied countries.