Democratic presidential hopefuls on Monday brandished their labor credentials before two of the nation's more powerful unions in a hunt for endorsements.

In Washington, Connecticut Sen. Chris Dodd cast himself as the alternative to the Democratic front-runners Hillary Rodman Clinton and Barack Obama, telling union activists that he's the only pro-labor candidate who can actually win the presidency in 2008.

"I know I'm not as well known, I know I'm not as well heeled," Dodd told a meeting of the Service Employees International Union. But "I know how to win elections."

Dodd, who is trailing in the Democratic polls, emphasized his long-term commitment to organized labor, saying he has pushed their issues for his entire 26 years in Congress. "I've been a union guy from the day I entered Congress, I'm a union guy today, and I'll be a union guy inside the White House," Dodd told the crowd of 1,500 purple-shirted union activists.

The SEIU endorsement would be a plum for any candidate. The organization bills itself as the nation's fastest growing union with more than 1.8 million members.

It is also a major player in campaign financing, having given more than $25 million to mostly Democratic candidates since 1989, according to the Center for Responsive Politics.

While Dodd was courting the SEIU in Washington, Clinton, former North Carolina Sen. John Edwards and Delaware Sen. Joseph Biden were vying for support from the 500,000-member Laborers' International Union of North America in Chicago.

Clinton also called herself a longtime labor supporter, while criticizing the Bush administration for policies she said create a "government of the few, by the few and for the few."

"There will be no invisible Americans when I am president," the New York senator told a roaring crowd of about 1,000 union members.

Edwards later told the group he wants "to be the president who is responsible for the greatest union growth in America."

"I want you to know I'll be with you when crunch time comes," Edwards said. "I'll be with you when it's hard. I have been in the past, and I will be in the future."

Dodd, Clinton and Edwards have each received endorsements from other unions this year.

SEIU President Andy Stern said he expects the service employees' endorsement to be made no earlier than October. However, the union members' reaction to the candidates Monday will play a big part in that decision.

"If they're all split up all over the place, it'll be hard to imagine the leaders making a decision," Stern said. "If they had a very strong preference for one of the candidates in September, it would have a huge positive impact on our decision making."

SEIU is one of seven major unions that broke from the AFL-CIO in 2005 over internal disagreements on how best to build organized labor's membership and political clout. The unions have since formed a new political coalition — Change to Win.

Only one of Change to Win's unions have made an endorsement: the United Brotherhood of Carpenters and Joiners, which endorsed Edwards last month. The rest will meet in Chicago later this month to hear from the Democratic primary candidates.