President Barack Obama delivers remarks at an Organizing for Action event held at the Mandarin Oriental hotel in downtown Washington, D.C., July 22, 2013. (KRISTOFFER TRIPPLAAR / POOL/EPA)

President Obama on Monday urged his most fervent supporters to channel their energies into bolstering a new White House focus on the economy and helping the middle class, describing their work on behalf of his agenda as even more important than his reelection campaign.

Addressing an invitation-only crowd of several hundred Organizing for Action volunteers, staff members and donors gathered at a Washington hotel for a day-long strategy session, the president said that the work of the past four and half years had succeeded in clearing “away the rubble” of the economic crisis.

“We’ve got back to a level ground, but now, we’ve got to keep climbing,” Obama said.

The president said that a speech he is set to give Wednesday will be aimed at refocusing Washington and the news media on the economy, but stressed that he needed grass-roots help to drive home his message.

“We’ve got to get folks activated and involved,” Obama said. “Ultimately, what you do day to day, away from the TV cameras, that is what is going to make a powerful difference.”

Monday’s summit marked the second time that Obama has addressed Organizing for Action, a nonprofit advocacy group launched by some of the president’s top advisers this year to promote his second-term priorities, built on the infrastructure and volunteer network from his reelection campaign.

“I miss all you guys!” the president declared to the whooping crowd, calling its work since his reelection “inspiring.”

Obama was joined at the event by Senate Majority Leader Harry M. Reid (Nev.), House Minority Leader Nancy Pelosi (Calif.) and Cecile Richards of Planned Parenthood, who told the group that it has the ability to change the political dynamic in Washington.

“Just think of the legacy that President Obama will have if he has more cooperation in the Congress,” Pelosi said.

The summit kicked off a month-long push by OFA dubbed “Action August,” in which the group plans to target lawmakers home for the summer recess on issues such as immigration reform, gun control and the environment. The month of activities starts Aug. 4, the president’s 52nd birthday, when OFA is set to hold events around the country promoting the implementation of Obama’s health-care overhaul.

“We are going to tell the story of how it is already benefiting people all across the country,” Executive Director Jon Carson told the gathering. “We are going to get the job done on Obamacare.”

The organization also will put a special focus on immigration reform, hoping to demonstrate a wave of support as the House takes up the issue.

“We are going to force it through the House,” said OFA Chairman Jim Messina, who ran Obama’s reelection campaign.

“I will sit with you and cry when Barack Obama signs his name on that law and millions of people come out of the shadows,” he added.

The sustained August campaign will test the impact of the organization, which has sought to apply the kind of grass-roots organizing that powered Obama’s reelection bid to issue advocacy.

Since it launched in late January, OFA supporters have held more than 6,500 events around the country — rallies, candlelight vigils, phone banking and letter-writing campaigns calling on Congress to pass tougher gun-control measures and approve a comprehensive immigration bill, among other issues.

While OFA leaders extolled the work of the group’s volunteers, the organization has struggled to demonstrate the substantive effect it is having on the legislative debate. And it has received criticism from local party officials for targeting four conservative Democrats who did not support stricter background checks for gun purchases.

The organization also had to halve its original goal of raising $50 million in its debut year after slower-than-expected fundraising and its decision to decline corporate donations. OFA reported raising $13.1 million through June, citing the support of more than 237,000 contributors who gave $55 on average.

At the summit, OFA leaders challenged the notion that they would not fulfill their mission.

“Of course, the naysayers are back saying, ‘Oh, change is hard,’ ” Messina said, adding, “You haven’t seen nothing yet.”

“I just need double the amount of work and two and half times the money,” he said. “We are off to a very fast start . . . but we’ve got to double down.”

Volunteers and staff members spent most of the day in training sessions and policy workshops, hearing from officials from a network of liberal and Democratic-aligned organizations such as the Center for American Progress, the Service Employees International Union and Planned Parenthood. Among the presenters was David Simas, deputy senior adviser for communications and strategy at the White House.

Ruth Tam contributed to this report.