WASHINGTON/NEW YORK (Reuters) - Former Vice President Joe Biden, in his first major foreign policy address as a Democratic presidential candidate, on Thursday blasted U.S. President Donald Trump’s performance on the world stage as erratic and extreme.

Trump, Biden told an audience in New York, has damaged America’s “reputation and our place in the world, and, I quite frankly believe, our ability to lead the world.”

The Republican president has unsettled Washington’s allies by withdrawing the United States from the Paris climate accord, a nuclear deal with Iran and a trans-Pacific trade agreement, and has also threatened to leave the North Atlantic Treaty Organization (NATO).

For Biden, who served eight years as Barack Obama’s vice president and 35 years in the U.S. Senate, it was a much-needed return to firmer ground after weeks of having to defend his civil rights record, while allowing him to train his attention on Trump rather than other Democrats.

Kamala Harris, a black U.S. senator from California, assailed the 76-year-old Biden in last month’s Democratic presidential debate over his past opposition to forced busing as a means to integrate schools and for remarks about his willingness to work with segregationists while in the Senate more than 40 years ago.

Biden apologized here for those remarks, but he has seen some erosion in support from Democratic voters, with Harris largely reaping the benefit and the field tightening in general among those vying to win the party's nomination to run against Trump in next year's general election.

In his address at the Graduate Center at the City University of New York, Biden criticized Trump for abdicating the United States’ leadership role in the world and argued that collective action is necessary to confront threats posed by climate change, nuclear proliferation, terrorism and cyberwarfare.

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“We must once more harness that power and rally the free world to meet the challenges facing us today,” Biden said. “It falls on the United States of America to lead the way.”

As president, Biden said he would pull most U.S. troops out of Afghanistan, end American support for Saudi Arabia’s military intervention in Yemen and reaffirm the nation’s commitment to NATO.

Biden reaffirmed his support for the security of Israel “regardless of how much you may disagree with its present leader” - a shot at Prime Minister Benjamin Netanyahu.

Domestically, Biden would terminate Trump’s travel ban against people from Muslim-majority countries and end the practice of separating migrant families at the U.S. border with Mexico.

Biden has sharply criticized Trump for walking away from the 2015 international nuclear deal with Iran, which Biden would reinstate should Tehran comply with its provisions.

As president, Biden would also have the U.S. rejoin the Paris Climate Accord and would convene a global summit on climate change.

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Biden would also push for more ironclad commitments from North Korea to abandon its nuclear program than Trump has so far demanded.

“Above all, diplomacy requires credibility,” Biden said. “Donald Trump has absolutely corroded our country’s credibility.”

For his part, Trump has not held back from criticism of the Obama administration’s foreign policy record. Trump has contended, among other things, that the Iran deal was too lenient and that Obama and Biden did not do enough to contain China’s economic aggression.

Ahead of Biden’s speech, the Republican National Committee and a pro-Trump Super PAC released lengthy critiques of Biden’s judgment on foreign affairs, pointing out that, among other things, Biden advised Obama to not go forward with the 2012 raid that killed Osama bin Laden.

Biden’s national security record has not yet been a front-burner issue among his rivals for the Democratic nomination, but his vote in favor of the invasion of Iraq while in the Senate has been denounced by U.S. Senator Bernie Sanders of Vermont and others.

At a campaign rally in Pennsylvania in May, Trump defended his “America First” policies, telling his supporters that Biden “said that he’s running to quote ‘save the world’ ... Well, he was: He was going to save every country but ours.”