DETROIT, Michigan — A fired-up US President Barack Obama Monday bluntly told Republicans to "show us what you got," stiffening his rhetoric ahead of his pivotal national address on jobs later this week.

Obama, seeking to restart stalled US job creation, revive the economy and his own tumbling political fortunes, issued his most strident challenge yet to rivals he accuses of putting political gain before their patriotic duty.

"Yes, times are tough. But we've been through tough times before," Obama told a pro-union crowd in a Labor Day speech in economically blighted Detroit.

"I don't know about you, but I'm not scared of tough times," said Obama, whose presidency is being stifled by huge unemployment and slowed economic growth as he tries to crank up his 2012 reelection bid.

Obama offered a glimpse of the initiatives he will offer in an address to the joint chambers of Congress on Thursday, confirming he would push for a scheme to repair infrastructure and for the extension of a payroll tax cut.

And despite partisan paralysis gripping Washington, Obama said he believed that Democrats and Republicans could still work together to create jobs.

"Given the urgency of this moment, given the hardship that many people are facing, folks have got to get together," he told a 13,000-strong crowd, which cheered him with chants of "four more years."

"But we are not going to wait for them," Obama said, in remarks likely to hearten some supporters who have questioned whether the president still has the stomach for a fight against his political enemies.

"We are going to see if we have got some straight shooters in Congress. We are going to see if Republicans will put country before party."

Facing the lowest approval ratings of his presidency, Obama was rattled on Friday by disastrous Labor Department data showing the stumbling economy created no jobs in August, at a time of 9.1 percent unemployment.

Obama said he would present Republicans in the House of Representatives with a plan to let construction laborers "get dirty" back at work, money in the paychecks of middle class Americans and to open up foreign trade markets.

"Show us what you got," he said, in a direct challenge to Republicans who oppose his economic plans and are determined to deprive him of a second term.

"The time for Washington games is over, the time for action is now. Now is not the time for the people you sent to Washington to worry about their jobs. Now is the time for them to worry about your jobs."

Obama offered a possible preview of his reelection strategy when he said he had been reading a speech by former US president Harry S Truman, who in 1948 ran a successful campaign lambasting the "do nothing Congress."

The annual Labor Day public holiday traditionally marks the formal start of campaigning when it falls on the year before a presidential election, and Obama's potential rivals are also seeking to make a Labor Day splash.

Former Massachusetts governor Mitt Romney is planning to lay out his own plan to create jobs this week, as the Republican race reaches new levels of intensity with a debate in California on Wednesday.

"We cannot continue on a course that has kept unemployment above eight percent for the longest stretch since records have been kept," Romney said in a statement.

"The potential of the American people has been demonstrated time and again. With leadership that understands how jobs are created, that potential can be unlocked -- that is why I am running for president of the United States."

Obama's speech on Thursday may represent his last chance to revive the economy before next year's presidential election goes into overdrive.

It will likely open a new rift with House Republicans who refuse to accept new spending proposals and tax rises and want steep cuts in expenditures in programs dear to Democrats in order to trim the deficit.

In addition to the infrastructure and payroll tax elements, the plan is expected to consist of a mix of old and new proposals, including a call for tax rises on the richest Americans.