More than 400 organizations, ranging from labor unions to faith, environmental and gay rights groups, expected tens of thousands of people to participate in the "One Nation Working Together" rally.
With a month of campaigning to go and voter unhappiness high, the Democratic-leaning groups are hoping that the four-hour program of speeches and entertainment will unify activists who are crucial if Democrats are to retain their majorities in the House and Senate.
Republicans are hoping to ride voter anger to victories in the November congressional elections and regain control of the House and possibly the Senate.
Organizers insist the rally is not partisan and say the message will be about job creation, quality education and justice. However, the largest of the organizers, such as the AFL-CIO and the Service Employees International Union, tend to back Democratic candidates.
A month ago, Beck and former Alaska Gov. Sarah Palin gathered near the Lincoln Memorial on the anniversary of Martin Luther King Jr.'s "I Have a Dream" speech to urge a vast crowd to embrace what they consider traditional values. Though also billed as nonpolitical, the rally was widely viewed as a protest against the policies of President Barack Obama and congressional Democrats.
One Nation organizers said that they began planning their event before learning about Beck's rally and that their march is not in reaction to it.
Obama planned to spend the weekend at Camp David, the presidential retreat in Maryland.