Cheered by Hollywood stars, President Barack Obama lampooned Mitt Romney's wealth and mined a shaggy dog story about his foe, striking a rare light note in the bitter White House race.

Obama used an annual star-studded dinner with White House correspondents and Hollywood A-listers, which presidents use to rip their rivals, to take a few gentle shots at Rommey, before the two rivals face off for the presidency.

He riffed off the hit movie the "Hunger Games" to poke Romney's hard bore Republican primary approach which he said saw "wealthy sponsors" brutally savage each other until only one contestant is left standing.

"I'm sure this was a great change of pace for him," Obama joked before a crowd of 2,000 journalists and celebrities on Saturday.

"Everybody is predicting a nasty election. And thankfully, we've all agreed that families are off-limits," Obama said, after a period when the two campaigns have feuded over the women's vote.

"Dogs, however, are apparently fair game," Obama quipped.

Romney has been dogged by Democratic supporters who keep bringing up the former Massachusetts governor's long-time ago family road trip when he affixed his family pet aboard the roof of his station wagon in a kennel.

As Obama spoke, a large screen in the ballroom of the Washington hotel hosting the dinner, pictured a mock-up of a dog kennel atop Air Force One.

Obama also jabbed Congress which has frustrated his job creation plans and most of the rest of his agenda since Congress seized the House of Representatives in 2010 mid-term elections.

"I've tried to be civil, to not take any cheap shots. And that's why I want to especially thank all the members who took a break from their exhausting schedule of not passing any laws to be here tonight," he said.