WASHINGTON DC, United States - Laughs were in short supply Wednesday as a somber President Barack Obama braved Comedy Central's biting "Daily Show" while his Democrats braced for a hammering from voters amid tough economic times.

Obama became the first sitting president to face off with Jon Stewart, host of the cable show, in a bid to reach out to his legions of young voters ahead of congressional polls on Tuesday that could see big Republican gains.

The show regularly skewers top politicians with withering humor and delights in exposing hypocrisy and insincerity but the mood was mostly serious on Wednesday, despite a studio audience that gave Obama a delirious reception.

"This notion that we could quickly transform Washington -- it's a work in progress, it's just not going to happen overnight," Obama said, though pleading for more time to deliver on the campaign for change he launched in 2008.

"When we promised during the campaign 'change you can believe in,' it wasn't change you can believe in, in 18 months."

"It was change you can believe in, but you know what, we are going to have to work for it," he added, mounting a fierce defense of policies designed to pull the United States out of its worst economic crisis in decades.

Obama also dismissed accusations that his signature health reform law, one of the most sweeping pieces of legislation in decades was "timid."

Stewart also gently mocked Obama over one of his campaign mantras to supporters that "we are the change we've been waiting for."

"Are we the people we were waiting for, or does it turn out those people are still out there -- and we don't have their number?" Stewart asked.

But the president replied: "I am feeling great about where the American people are, considering what we have gone through.

"We have gone through two toughest years of any time since the Great Depression."

Usually, the "Daily Show" consists of a satirical take on the day's news before a short guest segment, but Wednesday's show consisted of the first time that it had been devoted to a single guest, the White House said.

Obama's appearance was part of a run-up to Stewart's next big venture -- a "Rally to Restore Sanity," in American political life.

The event on Washington's central mall on Saturday is meant to lampoon the "Restore America" march led by right-wing icon Glenn Beck in Washington in August.

Stewart's alter-ego Stephen Colbert, another comedian, used his own fake news show on Comedy Central to invite Americans to attend another rally, which he dubbed the "March to Keep Fear Alive."