Tens of thousands of people rallied near the Lincoln Memorial in the US capital on Saturday as liberal groups attempted to energize their base a month before pivotal congressional elections.



The rally, held under sunny skies, was billed as "One Nation Working Together" and followed a large rally by conservatives at the same site just over a month earlier.



Richard Trumka, president of the AFL-CIO labor organisation, urged the crowd to "promise that you'll make your voices heard, for good jobs and justice and education today and on Election Day."



Republicans are trying to regain control of Congress from President Barack Obama's Democrats in the Nov. 2 congressional elections.



The rally was sponsored by unions, civil rights groups and liberal activists who have been struggling to get their messages heard during an election campaign in which media coverage has focused on voter anger over unemployment, a weak economy and government deficits.



Denise Gray-Felder, a spokeswoman for the organizers of the rally, estimated that 175,000 to 200,000 people attended.



Roxanne Bunnell, a 29-year-old student from Washington, D.C. who attended the rally, said she hoped it would get progressive voters riled up.



Opinion polls have indicated an election "enthusiasm gap," with Republican voters expressing more ardor about casting their votes than Democrats.



'FIGHT IN PACKS'



"Republicans are like dogs - they fight in packs and they're loyal," Bunnell said while holding a sign that read, "Stop the racist hate, Muslims are welcome here."



Democrats "need to be dogs, we need to pack up and we need to vote ... we need to spread that message," she said.



Many of those at the rally were derisive toward the loosely organized conservative Tea Party movement that has helped energize Republicans ahead of the mid-term elections.



One sign in the crowd read, "Axis of Ignorance Tea Party, Republicans, and Fox News," referring to the cable TV news channel that showcases many prominent conservatives.



Conservatives made a show of strength ahead of the elections with a rally headed by commentator Glenn Beck drawing tens of thousands of people at the same site on Aug. 28.



"I feel the liberal progressive voice of America has not been heard," said Michelle Ridley, a 39-year-old recruiter for a federal government contractor from Gaithersburg, Maryland.



Ridley said she came out to show support for healthcare reform and Obama.



While many at the rally said they support the Democrats and the Obama administration, some expressed disappointment that Democrats had not done more on issues they care about like healthcare reform.



Civil rights leader Al Sharpton told the rally crowd - which stretched from the Lincoln Memorial to the end of the National Mall's Reflecting Pool - to consider the congressional elections a "mid-term exam."



"We've got to go home, and we've got to hit the pavement. We've got to knock on doors. We've got to ring that church bell. We've got to get ready for the mid-term exam," he said.



Obama used a series of appearances around the country earlier this week to try to fire up his party's supporters ahead of the November 2 elections. Republican control of Congress could sidetrack Obama's legislative agenda.