Joe Biden to address UN General Assembly for the last time as president

US President Joe Biden will look to burnish his foreign policy legacy in a UN speech on Tuesday, still facing the challenges posed by Ukraine's effort to repel Russian invaders and in a Middle East mired in war.

With four months left in office, Biden steps up to the green-marbled lectern to address world leaders at the UN General Assembly with wars in both regions posing dilemmas likely to outlast his presidency.

As efforts falter to impose a Gaza truce and with Israel and Lebanon's Hezbollah waging a cross-border battle, the Pentagon said on Monday it will send a small number of additional troops to the Middle East out of an abundance of caution.

Biden's presidency has been dominated by foreign policy challenges from Russia's February 2022 invasion of Ukraine to the Palestinian Hamas attack in southern Israel and hostage-taking last Oct 7 and the resulting Israeli assault on Gaza.

Countering China and Iran, which backs both Hamas and Hezbollah, have consumed major chunks of the president's time.

A senior administration official said Biden's speech at 10 a.m. EDT (1400 GMT) will give him an opportunity to talk up what he considers major achievements of his time in office and to say the international community should support Ukraine and a diplomatic solution is needed in the Middle East.

White House press secretary Karine Jean-Pierre told reporters on the Air Force One flight to New York that Biden will outline his "vision for how the world should come together to resolve these big problems and defend fundamental principles such as the U.N. Charter."

Biden is due to hear from Ukraine President Volodymyr Zelenskiy about a new Ukrainian peace plan when they meet in Washington on Thursday. A U.S. official said the plan is probably much like previous plans calling for more weaponry and support for Ukraine's fight.

"We support Ukraine's pursuit of a just, lasting and comprehensive peace to this war. And the president is committed to providing the Ukrainian military with the equipment they need to strengthen their position," Jean-Pierre said.

Biden's UN speech will be the centerpiece event of a two-day visit to New York that includes a climate speech later on Tuesday and a meeting on Wednesday with To Lam, the president of Vietnam.

Biden has been eager to deepen relations with the strategic Southeast Asian country and manufacturing hub to counter Russia and China, with which Vietnam also retains ties.

Ukraine and Russia, Gaza, Iran and China all figure to linger on as challenges for the next president, whether Biden's successor is his vice president, Kamala Harris, a Democrat, or former President Donald Trump, a Republican.

Harris' approach to foreign policy is much like Biden's, although she has struck a tougher tone on the tens of thousands of Palestinian deaths and the humanitarian crisis in a Gaza Strip devastated by a nearly year-long Israeli assault.

Trump, professing more isolationist tendencies, has little enthusiasm for supporting Ukraine's battle to expel Russian invaders and is a firm backer of Israeli Prime Minister Benjamin Netanyahu, who has frayed relations with Biden.

Biden has expressed steadfast support for Israel in its drive to eliminate Hamas militants from Gaza but so far has been unsuccessful in his bid to negotiate a ceasefire-for-hostages deal and no breakthrough is in sight.

Under Biden's leadership, the United States has funneled millions of dollars in American weaponry to Ukraine and rallied NATO solidarity behind Kyiv. But the conflict is largely at a stalemate with Russia hanging on to parts of eastern Ukraine it seized early in the war