Mr. Trump has broadly criticized how the United States distributes foreign aid, and some conservative Middle East policy analysts have argued that aid to the Lebanese military could end up helping Hezbollah.

One congressional official said it was troubling that the White House had ordered the action against the recommendations of both the State and Defense Departments. The official said that the United States closely monitors how the aid is used, and that any fear that the money could fall into the hands of Hezbollah is a myth.

In December, Jim Mattis, who was defense secretary at the time, described the Lebanese Army Forces as “legitimate” and a partner of the American military. “They are helping to keep the situation stable right now,” he said, speaking of a flare-up in tensions between Hezbollah and Israel, two longtime enemies.

Other top American officials have given similar assessments. David Schenker, the State Department’s new assistant secretary of near eastern affairs, argued in an August 2017 paper that, although the Lebanese military had been “colluding” with Hezbollah, it had helped stabilize the country and repel militant Sunni influence. Earlier that year, General Joseph L. Votel, then the leader of United States Central Command, told the Senate Armed Services Committee that the Lebanese army had “demonstrated tremendous return on investment in recent years,” and that Washington should consider increasing its support.

Analysts said Friday that the United States was acting against its own goals by withdrawing the aid, especially at a time when Lebanese protesters are also questioning why the United States has stood by Lebanon’s government, which they oppose. Severing ties with the Lebanese army could create an opening for other sources of money, notably Iran or Russia, whose power in neighboring Syria has increased since Mr. Trump withdrew American troops last month from the Syria-Turkey border region.

“We still have U.S. interests in the region, and losing our toehold there — no matter how slim it may be now — will prevent us, in the future, from steering things in a better way for us and for Lebanon,” said David Daoud, a Hezbollah analyst at United Against Nuclear Iran, which advocates tougher United States policies on Iran.

“Does that mean we should be O.K. with what the L.A.F. is doing now?” he added. “Absolutely not. There should be more accountability, there should be a little bit more tough love, but to cut off the aid would be, I think, counterproductive for our interests.”