Democratic candidate Hillary Clinton criticized rival Barack Obama as a big dreamer with little substance on Wednesday as she sought to slow his momentum from 10 straight victories in the race for the party's U.S. presidential nomination.

"We need to dream big, but you know, dreams alone won't make anything," Clinton said while courting Hispanics at a noisy rally in this south Texas town on the Mexican border. "We've got to have solutions to the problems that face us."

The New York senator and former first lady sharpened her message against Obama before the March 4 Democratic nominating contests in Texas and Ohio, which have become critical to her presidential aspirations after losses to Obama in Wisconsin and Hawaii.

But support mounted for the first-term Illinois senator, whose "yes we can" message and powerful speaking style has propelled him to the front-runner's position. The 1.25 million member Teamsters union formally endorsed him on Wednesday.

His long string of victories put Clinton in the awkward position of telling supporters, in media interviews and speeches, "Don't give up on this!" and "This campaign goes on!" while her aides explained how she would close the gap with Obama by the time of the Puerto Rico contest in June.

She and Obama crisscrossed Texas on Wednesday and will face off in a crucial debate on Thursday in Austin.

In the Republican race, likely nominee John McCain's campaign angrily rejected a report in The New York Times that he had a close relationship with a female lobbyist eight years ago that the paper suggested had undermined his stance as a promoter of high ethics among lawmakers.

The Times said both had denied a romantic relationship.

McCain spokeswoman Jill Hazelbaker called the report "a hit and run smear campaign."

"Americans are sick and tired of this kind of gutter politics," she said. "And there is nothing in this story to suggest that John McCain has ever violated the principles that have guided his career."

Analysts believe Clinton can only turn around her campaign by winning big victories in two weeks in Texas and Ohio. Her husband, former President Bill Clinton, basically agreed.

"If she wins in Texas and Ohio I think she will be the nominee," he said. "If you don't deliver for her, then I don't think she can. It's all on you," he told supporters in Beaumont, Texas.

Obama has used his string of wins to broaden his voting coalition and has taken control of the race to decide the Democratic nominee for the November election. He has victories in 25 of the state-by-state contests while Clinton has 11, and he has begun to erode support among her core base of women.

At a fund-raising event in New York, Clinton belittled Obama as an inexperienced choice for commander-in-chief in a dangerous world, for advocating a health care plan that is not as expansive as hers and for giving airy speeches.

"It's about picking a president who relies not just on words but on work, on hard work," she said.

BUILDING A NATIONAL LEAD

Obama rejected her criticisms while campaigning in Texas, telling a crowd of some 17,000 in Dallas Clinton was right that the race was about choices but wrong about everything else.

"It's a choice between a politics that offers more of the same divisions and distractions that didn't work in South Carolina and didn't work in Wisconsin and will not work in Texas. Or a politics of common sense, of common purpose, of shared sacrifice and shared prosperity."

Underscoring Clinton's high negative ratings in public opinion polls, he added: "It's a choice between going into the general election with Republicans and independents already united against us or running with a campaign that has already united Americans of all parties around the agenda for change. That's the choice."

A new Reuters/Zogby poll indicated Obama has leaped past Clinton and built a big national lead.

The poll showed Obama, who would be the first black president, with a 14-point edge over Clinton, 52 percent to 38 percent, after being in a statistical tie with the New York senator last month.

In the border town of Hidalgo, Clinton also took aim at President George W. Bush, the Texan who has 11 months left in office. "Don't you think the entire world will let out a sigh of relief" when he leaves office? she asked. The crowd cheered.

Texas and Ohio offer a rich trove of 334 delegates to the Democratic nominating convention this summer, giving Clinton the chance to catch up with Obama after falling behind in the delegate count.

Clinton also seemed to take a shot at Obama's wife, Michelle Obama, after Mrs. Obama raised eyebrows by saying this week in Wisconsin she felt pride in the United States for the first time in her adult life because it felt like hope was returning to the nation.

"This country has given me so many opportunities," Clinton said. "I am proud of the United States of America."