WASHINGTON, District of Columbia (AFP) - President Barack Obama expressed concern in an interview published on Sunday over widening income inequality and an erosion in upward mobility that he said is leading to a fraying of American society.

Obama told the New York Times that a growing gap between rich and poor and the lack of opportunities for average Americans to get ahead represents a sharp break with a long-held social compact which is central to the national identity.

Upward mobility once "was part and parcel of who we were as Americans," Obama told The Times.

"That's what's been eroding over the last 20, 30 years - well before the financial crisis." "If we don't do anything, then growth will be slower than it should be. Unemployment will not go down as fast as it should. Income inequality will continue to rise," Obama said.

"That's not a future that we should accept."

The remarks echo comments he made this past week during a campaign-style swing in which he challenged a hostile Congress to work with him to restore middle class prosperity.

During stops in Illinois, Missouri and Florida, Obama made a robust defence of his stalled economic initiatives, which have been bottled up in the Republican-led House of Representatives.

The president said the financial meltdown of several years ago is still having a negative economic impact on middle and working class Americans, who already have been losing ground for at least a generation.

Obama's efforts to reinitiate a debate over the economy comes with Congress reloading for a new round of battles over spending cuts and raising the debt ceiling.

He has touted his administration's rescue of the auto industry, its health care reforms and its shoring up of the financial sector, among other achievements that have helped turn the economy around.

But it is vitally important, he said, that ordinary American reap the benefits of economic resurgence.

"If the economy is growing, everybody feels invested. Everybody feels as if we're rolling in the same direction."

While the economy is "far stronger" than when he took office four years ago, Obama said average Americans still do not feel secure about their future," saying middle class people in the country are "anxious" and "frustrated."

The president is bracing for renewed clashes with Republican lawmakers over the budget, battles which threaten to hurt the economy anew.

Republicans accuse Obama of offering nothing but higher spending and bigger government, and on Wednesday Republican House leader John Boehner mocked the president's latest initiative.

The president hopes to negotiate a new budget compromise by October - the end of the current fiscal year - in order to head off the threat of a government shutdown.

As the November 2014 midterm elections loom in the distance, a new standoff over the US debt ceiling looks increasingly likely.

Obama told The Times that he is eager to work with his Republican opponents - if they show the willingness and flexibility to work with him.

"I will seize any opportunity I can find to work with Congress to strengthen the middle class, improve their prospects, improve their security," the president said.

But he added that he would not back down from a fight with his Republican opponents.

"I'm not just going to sit back if the only message from some of these folks is no on everything, and sit around and twiddle my thumbs for the next 1,200 days."