Nevada’s Democratic caucuses on January 19 are set to be too close to call, as both Senators Clinton and Obama hurried to the Silver State to shore up their support.

While Mr. Obama reveled in his endorsement from the local restaurant workers’ union, Mrs. Clinton was in the gambling vacation city of Las Vegas, addressing widespread anxiety among blue-collar workers about the faltering economy with her plan to halt home foreclosures.

While the Clinton camp was dampening expectations and stressing that their candidate could comfortably win the nomination despite losing Nevada and South Carolina, her Nevada spokeswoman, Hilarie Grey, did not play down the significance of her winning. “It’s important because it’s the first voice in West. We expect to see Senator Clinton here a lot over the last 11 days,” she told the Reno Gazette-Journal.

Mr. Obama’s Nevada campaign boasted “thousands of energized volunteers,” and Senator Edwards’s Nevada spokesman, Adam Bozzi, was left insisting that the primary remained a three-way race. “We are absolutely competing in Nevada,” he said.

The pivotal contest, the first since Mrs. Clinton’s unexpected victory in New Hampshire, has been set up by Mr. Obama as a David and Goliath battle between the Democratic establishment in Nevada, who have come out in favor of Mrs. Clinton, and his grass-roots insurgency.

But that carefully drawn contrast was dealt a blow yesterday when a pillar of the Democratic Party and the losing 2004 presidential candidate, Senator Kerry, endorsed Mr. Obama in South Carolina with a warm embrace.

Mrs. Clinton, who has been enjoying poll leads upward of 20% for more than a year, was leaving little to chance and last night in Las Vegas went door to door canvassing voters in their homes before speaking about her remedy for the crumbling housing market.

With the race narrowing sharply, Mr. Obama, who arrives in Las Vegas on Friday, is trying to portray himself as being as worldly wise as Mrs. Clinton by mounting a foreign policy seminar at the University of Nevada, Reno.

Mr. Obama — whose surrogates have been questioning the sincerity of Mrs. Clinton’s concern for black Americans by raising her response to the Katrina flooding in New Orleans — saw an opportunity in a crumbling levee that flooded Fernley, Nev., over the weekend, driving 1,500 from their homes.

Mrs. Clinton said she was “deeply concerned and saddened” at the event, but Mr. Obama went one better. “I have asked my staff and supporters in the area to take time out from campaigning this weekend to assist in the relief efforts,” he announced.

Yesterday brought more intense competition between the candidates. Formal backing for the former Chicago hotel workers’ organizer, Mr. Obama, came from Culinary Local 226, representing 60,000 Nevada hospitality industry workers, adding to the endorsement on Monday of the 17,500-strong Service Employees International Union representing health care and public sector employees.

Mrs. Clinton, meanwhile, welcomed the endorsement of a House lawmaker, Rep. Shelley Berkley, which led D. Taylor, secretary-treasurer of the culinary union branch, to tell his members, “We understand that we’re going against the entire Democratic power structure. … But the last time I looked, it was the people who voted, not them.”

Union support for Mr. Obama brought into question the wisdom of Mr. Edwards’s decision in last weekend’s debate to side with the Illinois senator, thereby splitting the anti-Clinton vote. An explanation for the decision by SEIU’s executive director, Jane McAlevey, cannot have been comfortable for the trial lawyer to hear. “I think there’s a broad assessment that [the Edwards] candidacy is not viable,” she told the Las Vegas Sun. “His entire strategy was, he had to get a bump out of Iowa. It really is going to be a decision between Clinton and Obama.” Mr. Edwards will spend most of next week in South Carolina, the state in which he was born, which votes on January 26.

Mr. Taylor issued a reminder that the Nevada caucuses were brought forward by the party to better reflect the complexion of the Democratic base.

“I have a lot of respect for all those folks in Iowa and in New Hampshire,” he said, to chants of “Si se puede [Yes we can],” Mr. Obama’s slogan in Spanish. “We’re not just Wonder Bread. We’ve got pumpernickel. We’ve got whole wheat. We’ve got rye. That’s America. That’s why Senator Obama excites us and excites the country.”

Nevada’s racial mix may prove the key to the result. Whereas in Iowa Hispanics are 3.5% of the population and in New Hampshire 2.1%, they are 22.8% in Nevada. Hispanics make up 60% of union membership, though many are not registered voters. The decision of Governor Richardson of New Mexico to withdraw may also prove important. He polled 7% in the most recent poll, enough to make the difference in a tight contest.