WASHINGTON (AFP) - Barack Obama on Wednesday returned to the core economic philosophy of middle class opportunity on which he has centered his presidency, as he strives to exit a second term slump.

The US leader struck economic themes familiar from his two presidential campaigns as he sought to steady his administration after self-inflicted wounds over his health care law which have seen his popularity slide.

Speaking in Washington at the Center for American Progress think tank, Mr Obama bemoaned "a dangerous and growing inequality and lack of upward mobility" in US life that has harmed what he has often described as the nation's basic bargain - anyone who works hard has a chance to get ahead.

"I believe this is the defining challenge of our time: making sure our economy works for every working American," Mr Obama said. "That's why I ran for president. It was the center of last year's campaign. It drives everything I do in this office."

Mr Obama struck similar notes during his 2008 campaign and they proved potent to an even greater extent in his reelection race against Republican Mitt Romney last year.

Mr Obama is delivering a series of speeches and holding political events as part of a bounce back strategy after a miserable two months since the botched launch of a website for his signature health care law.

He is seeking to rally his personal political base and to appease Democratic lawmakers who are concerned his ebbing fortunes could damage their prospects in mid-term elections next November.