By James Oliphant

LOS ANGELES (Reuters) - Hillary Clinton has captured enough delegates to secure the Democratic presidential nomination, according to tallies by two U.S. media outlets, as she and rival Bernie Sanders face off on Tuesday in contests in six states, including Montana.

A former senator and U.S. secretary of state, Clinton would be the first woman to ever be


the presidential candidate of a major political party in the country's history.

Sanders has vowed to keep up the fight in what has been a long and increasingly antagonistic Democratic primary race.

The U.S. senator from Vermont, who calls himself a democratic socialist, has commanded huge crowds spilling out of parks and stadiums, galvanizing younger voters with his promises to address economic inequality.

But Clinton has continued to edge out Sanders, particularly among older voters with longer ties to the Democratic Party. Her less lofty promises focus on improving upon the policies of her fellow Democrat and former boss, President Barack Obama.

On Tuesday morning, Clinton secured the endorsement of House of Representatives Democratic leader Nancy Pelosi of California, who noted Clinton's career devoted to children and working families.

"In this campaign, we have seen her vision, her knowledge, her ability, indeed her stamina, to get the job done for the American people," Pelosi said in a statement.


After the Associated Press and NBC reported on Monday night that Clinton had clinched the number of delegates needed to win her party's nomination, a Sanders campaign spokesman castigated what he said was the media's "rush to judgment."

Under Democratic National Committee rules, most delegates to the party's July 25-28 convention are awarded by popular votes in state-by-state elections.

But the delegate count also includes "superdelegates" - party leaders and elected senators, members of Congress and governors - who can change their mind at any time.

For that reason, the DNC has echoed the Sanders campaign, saying the superdelegates should not be counted until they actually vote at the Philadelphia convention.

But that has not deterred the news media. The AP and NBC reported that Clinton reached the 2,383 delegates needed to become the presumptive Democratic nominee with a decisive weekend victory in Puerto Rico, a U.S. territory, and a burst of last-minute support from superdelegates.

"According to the news, we are on the brink of a historic, historic, unprecedented moment," Clinton told a rally in Long Beach, California, shortly after the AP report.

"But we still have work to do, don't we? We have six elections tomorrow and we're going to fight hard for every single vote, especially right here in California."

Michael Briggs, Sanders' spokesman, dismissed the AP and NBC tallies.

"Our job from now until the convention is to convince those superdelegates that Bernie is by far the strongest candidate against Donald Trump," he said.

California, New Jersey, Montana, North Dakota, South Dakota and New Mexico hold nominating contests on Tuesday.

The outcome in California, the last and largest state to vote, could affect Clinton's efforts to unify the party behind her.

If Sanders, who was trailing in polls in California until recently, roars back to take the state, he may have little incentive to exit the race despite increasing pressure from party luminaries to stand down.

Clinton spent Monday working to turn out Hispanic and African-American voters - demographic groups that have provided a pillar of support for her during the nominating process.

She spent the day in Southern California, first in the heavily Latino city of Lynwood, then later in central Los Angeles, speaking before throngs of black supporters.

Sanders, meanwhile, campaigned in the San Francisco Bay Area.

Sanders' supporters have become increasingly resistant to Clinton in recent months, with fewer than half saying they would vote for her if she becomes the party's nominee, according to a Reuters/Ipsos poll in May.

Last month, 41 percent of Sanders' supporters said they would vote for the former secretary of state if she runs against Trump in the Nov. 8 general election. That was down from 50 percent in April, and 52 percent in March.

Those who have decided not to support Clinton are split on what to do if Sanders quits the race. Some may cross party lines and vote for Trump, but many others appear to be interested in a third-party candidate. Some 27 percent of Sanders' supporters said in May that they would vote for neither candidate or another alternative.

One Sanders supporter, Andrew Swetland, 31, an accountant from Long Beach, said he would not vote for Clinton if she heads the Democratic ticket.

“We're tired of all the things the establishment in the party is trying to force on us,” he said, adding that he would support the Green Party's Jill Stein instead.

The Reuters/Ipsos poll included 2,919 Sanders supporters during the month of May and has a credibility interval, a measure of accuracy, of 2 percentage points.

(Additional reporting by Ginger Gibson, Jonathan Allen, Amanda Becker and Chris Kahn; Editing by Caren Bohan, Robert Birsel)