By Jeff Mason and Valerie Volcovici

WASHINGTON, April 22 (Reuters) - The Biden administration on Thursday pledged to slash U.S. greenhouse gas emissions by 50%-52% from 2005 levels by 2030, a new target it hopes will spur other big emitter countries to raise their ambition to combat climate change.

The goal, unveiled at the start of a two-day climate summit hosted by Democratic President Joe Biden, comes as the United States seeks to reclaim global leadership in the fight against global warming after former President Donald Trump withdrew the country from international efforts to cut emissions.

It also marks an important milestone in Biden's broader plan to decarbonize the U.S. economy entirely by 2050 - an agenda he says can create millions of good-paying jobs but which many Republicans say they fear will damage the economy.

The emissions cuts are expected to come from power plants, automobiles, and other sectors across the economy, but the White House did not set individual targets for those industries.

"It's an economy-wide goal. There are going to be multiple pathways to get there," one official told reporters on a conference call describing the plan.

Sector-specific goals will be laid out later this year.

How the United States intends to reach its climate goals will be crucial to cementing U.S. credibility on global warming, amid international concerns that America's commitment to a clean energy economy can shift drastically from one administration to the next.

Biden's recently introduced $2 trillion infrastructure plan contains numerous measures that could deliver some of the emissions cuts needed this decade, including a clean energy standard to achieve net zero emissions in the power sector by 2035 and moves to electrify the vehicle fleet.

But the measures need to be passed by Congress before becoming reality.

Biden focused on restoring U.S. climate leadership during his campaign and in the first days of his presidency after Republican Trump, a climate change skeptic, removed the United States from the Paris agreement on global warming.

The new administration has come under heavy pressure from environmental groups, some corporate leaders, the UN secretary general and foreign governments to set a target to cut emissions by at least 50% this decade to encourage other countries to set their own ambitious emissions goals.

Biden will announce the number at the start of a climate summit on Thursday that will be attended by leaders from the world's biggest emitters, including China.

World leaders aim to limit global warming to 1.5 degrees Celsius above pre-industrial levels, a threshold scientists say can prevent the worst impacts of climate change.

One of the administration officials said with the new U.S. target, enhanced commitments from Japan and Canada, and prior targets from the European Union and Britain, countries accounting for more than half the world's economy were now committed to reductions to achieve the 1.5 degrees Celsius goal.

"When we close this summit on Friday, we will unmistakably communicate ... the U.S. is back," he said.

(Reporting by Jeff Mason and Valerie Volcivici; Editing by Lisa Shumaker)