UNITED NATIONS — President Donald Trump used his United Nations debut on Monday to prod the international organization to cut its bloated bureaucracy and fulfill its mission. But he pledged U.S. support for the world body he had excoriated as a candidate, and his criticisms were more restrained than in years past.

“In recent years, the United Nations has not reached its full potential due to bureaucracy and mismanagement,” Trump said. “We are not seeing the results in line with this investment.”

The president urged the U.N. to focus “more on people and less on bureaucracy” and to change “business as usual and not be beholden to ways of the past which were not working.” He also suggested the U.S. was paying more than its fair share to keep the New York-based world body operational.

The short remarks at a forum on U.N. reforms were a precursor to Tuesday’s main event, when Trump will address the U.N. General Assembly for the first time, a speech nervously awaited by world leaders concerned about what the president’s “America first” vision means for the future of the world body.

Trump riffed on his campaign slogan when asked to preview his central message to the General Assembly, saying: “I think the main message is ‘make the United Nations great’ — not ‘again.’ ‘Make the United Nations great.”’

“Such tremendous potential, and I think we’ll be able to do this,” he added.

But even as the president chastised the U.N., he pledged that the United States would be “be partners in your work” to make the organization a more effective force for peace across the globe.

He praised the U.N.’s early steps toward reform and made no threats to withdraw U.S. support. The president’s more measured tone stood in sharp contrast to the approach he took at NATO’s new Brussels headquarters in May, when he scolded member nations for not paying enough and refused to explicitly back its mutual defense pact.

While running for office, Trump had labeled the U.N. as weak and incompetent, and not a friend of either the United States or Israel. But he has softened his message since taking office, telling ambassadors at a White House meeting in April that the U.N. has “tremendous potential.”

Trump more recently has praised a pair of unanimous U.N. Security Council votes to tighten sanctions on North Korea over its continued nuclear weapons and ballistic missile tests.

The annual gathering of world leaders opens amid serious concerns about Trump’s priorities. For many world leaders, it will be their first chance to take the measure of the president in person.

The president Monday praised U.N. Secretary-General Antonio Guterres, who said he shared Trump’s vision for a less-wasteful U.N. that will “live up to its full potential.” The U.S. has asked member nations to sign a declaration on U.N. reforms, and more than 120 have done so.

His speech began a busy week of diplomacy for Trump, who is scheduled to meet separately with more than a dozen world leaders along the sidelines of the U.N. In his first bilateral meeting, with Israeli Prime Minister Benjamin Netanyahu, Trump declared that they “are giving it an absolute go” on Middle East peace talks.