HIDALGO, Texas -- The Dodge Sports Arena was only two-thirds full, but the mariachi bands were deafening, the crowd exuberant, the candidate unbowed.

One day after suffering a crushing loss in the Wisconsin primary and with national polls showing Illinois Sen. Barack Obama leading her by double digits, New York Sen. Hillary Rodham Clinton flew to a pair of rallies last night in South Texas, where she hammered on the differences between her and her Democratic rival.

"People ask me, 'What are the differences between you and your opponent in this election?' she asked, as she exhorted the crowd to take advantage of the state's early voting.

"I'm going to provide health care to everyone. I don't want to leave anyone out, while Sen. Obama leaves out 15 million," she said, in what has become a familiar charge. "We don't need on-the-job training for the next president of the United States."

Her appearances in the U.S. border towns of Hidalgo and Brownsville came the night before she faces off in a nationally televised debate in Austin with Mr. Obama, who has bested her in the last 10 primary contests. That debate, sponsored by CNN at the University of Texas, is one of the last opportunities she will have to draw the differences between her candidacy and his.

Along with Ohio, the March 4 primary in Texas is a must-win for Mrs. Clinton, whose campaign spent much of yesterday battling to squelch talk that Mr. Obama has seized the upper hand in the party's presidential nomination race. She made no mention of her primary defeats in her talk to supporters.

Mrs. Clinton heads into tonight's crucial debate grasping for some gambit or Obama gaffe that would shake up the dynamics of a contest in danger of slipping beyond her control. Even her supporters acknowledged that time was short.

"At least she's going down fighting," said supporter Nancy Reyes, 33, of MacAllen. "That shows so much. She's gone through so much, and she's still standing."

On a conference call with reporters yesterday, David Plouffe, the Illinois senator's campaign manager, maintained that Mrs. Clinton would have to win each of the three big states on which she is pinning her hopes -- Texas, Ohio and Pennsylvania -- by margins approaching 65 percent to allow her to begin to close the gap in pledged delegates after Tuesday's contests. Mr. Plouffe said his campaign now had an edge of 159 pledged delegates.

"I am amused when the Clinton campaign continues to say it's essentially a tie -- that's lunacy," he said.

As is often the case in politics, good news engendered more good news for the Obama camp yesterday, as the string of victories that culminated in the Wisconsin landslide helped attract an endorsement from the International Brotherhood of Teamsters.

Howard Ickes, Mrs. Clinton's chief delegate counter, insisted that his candidate would win in Texas, Ohio and, later, in Pennsylvania, although he would not speculate about how big a margin she might gain.

The Obama campaign, on the other hand, suggested that they would win by losing -- in that a narrow overall victory for Mrs. Clinton in any of those states would produce a net gain of only a handful of delegates.

"If one of us were to win Ohio by less than five points," Mr. Plouffe said, "the likely outcome is a pledged delegate net of only three."

He speculated further that the complex, hybrid primary/caucus system in Texas could allow one candidate to win the popular vote while the other picks up a greater number of delegates.

Mrs. Clinton's Texas director, Ace Smith, insists that that won't happen. Speaking to reporters earlier this week, he said the Clinton campaign had precinct captains in place in 4,000 of the state's 8,300 precincts. With roughly 20 field offices across the state, he said, "we're going to have a ground operation people haven't seen. ... In California, we beat Barack Obama among young voters; we intend to do the same in Texas."

The caucus process has played to the Obama campaign's organizing strength in previous state contests, but Mr. Smith said the Clinton grass-roots effort would reverse that trend in two weeks. In the meantime, he said, the campaign would focus relentlessly on drumming up the early votes that are permitted in Texas and Ohio.

"We have ads up featuring [former San Antonio Mayor and U.S. Housing and Urban Development] Secretary [Henry] Cisneros urging people to early vote," he said in a conference call Tuesday. "It's going to be a huge part of what you're going to see us doing." Mr. Cisneros served in former President Bill Clinton's Cabinet.

Looking at the longer term, his colleague, Mr. Ickes, again reminded reporters that neither Democrat was in a position to clinch the nomination on the strength of pledged delegates alone and will need to turn to the superdelegates -- or automatic delegates, as the Clinton campaign describes them -- to win the party's nod.

"Both candidates will need a number of automatic delegates to clinch the nomination," Mr. Ickes said. "We think Mrs. Clinton will be able to get those about the time [of Puerto Rico's June 7 caucuses] or shortly thereafter."

Mrs. Clinton has made a point of courting Hispanics in her quest for the nomination. Nationally, they make up about 35 percent of the Democratic primary electorate. And among Hispanic voters in the Rio Grande Valley border towns -- Edinburg, McAllen and Hidalgo -- especially among older women and working-class voters, she is very popular.

Right at the outset, she noted, as she has in most of her speeches in Texas, her longtime connections to this part of the state -- during the 1972 campaign of Democrat George McGovern, she registered voters in the Rio Grande Valley -- and her husband, the former president, is fondly remembered here.

"I feel so strongly about my relationships, my history here," she said, as the crowd roared. "Thirty-six years ago, going door to door, registering voters, asking people to be involved, is something I value so greatly. You may have noticed I love coming to South Texas."

Speaking to the crowd in Hidalgo, Mr. Cisneros said: "This is a profoundly important election. ... This is not a game. This is not just about the glitziness of a campaign. It's personal. She will make history."