WASHINGTON - A defiant President Barack Obama campaigned for an endangered Democratic congressman Friday as he tried to rally his party nationwide to prevent big gains by Republicans in Tuesday's elections.

His efforts were shadowed by fresh news of a weak economy still struggling to create jobs and a terror probe on three continents.

Predictions of a Republican election blowout dogged the president and his party, as voters looked to take their anger out on incumbents over joblessness, bailouts and the toxic state of politics. Republicans were looking to recover from recent electoral lashings by claiming the House and making big gains in the Senate, governors' mansions and state legislatures.

Obama was campaigning for Tom Perriello, a first-term congressman who won by the narrowest of margins two years ago and then loyally backed Obama on signature bills to spur the economy and overhaul health insurance. Obama was addressing a nighttime rally in the college town of Charlottesville, Virginia.

"The reason I am here is because in this day and age, let's face it, political courage is hard to come by," Obama said to thousands gathered outside on a crisp autumn night. "When you're a first-term congressman, the easiest thing to do is make your decisions based on the polls ... That's not who Tom is."

The stop was meant as more than a boost for Perriello, who is in a fierce election fight against Republican state Sen. Robert Hurt. The president also wanted to send a message to fellow Democrats and ambivalent supporters that not only would he stand with those who took tough votes to support his agenda, but that his party should not be embarrassed by its record of the past two years such as passing landmark health care reform legislation.

"It's clearly payback for being a loyal foot soldier for the Pelosi-Obama agenda," shot back Hurt, referring to House Speaker Nancy Pelosi, who stands to lose that leadership position should Republicans pick up the 40 seats they need in the House of Representatives.

The Republicans expect to pick up many of those seats in usually Republican-leaning districts like Perriello's which narrowly swung into the Democratic column in 2008 when voters upset over the plummeting economy under President George W. Bush elected Obama with large congressional majorities.

All 435 House seats and 37 of the 100 Senate seats are on the ballot. The Republicans need to gain 10 seats to take control of the Senate.

The White House said Obama's final round of campaigning for Tuesday's elections would not be affected by the international terror probe. Obama's itinerary includes stops in Philadelphia and Chicago, both cities involved in the investigation into suspicious packages sent to the U.S. from Yemen.

Packages containing explosives in Dubai and England were addressed to Jewish organizations in the Chicago area. A plane was also investigated at Philadelphia's airport because it was believed to contain cargo from Yemen.

Ahead of Tuesday's election, official early voting tabulations showed more than 11.6 million voters had already cast ballots, including more than 2 million in California, 1.6 million in Florida and 1.2 million in Texas.

There also were high totals in other states where races were particularly intense: including nearly 675,000 in Colorado, where Democratic Sen. Michael Bennet is in a close contest with Republican challenger Ken Buck.

In Nevada, more than 339,000 ballots had been cast in an early voting period, shattering the total of 244,000 in the midterm election four years ago. The state has the country's most closely watched Senate election, pitting Majority Leader Harry Reid against Republican Sharron Angle, who won her nomination on the strength of support from the grass-roots conservative-libertarian tea party movement.

The results of the elections seem sure to alter the course of Obama's presidency and change the debate on issues that matter to tens of millions of people: taxes, education, immigration, energy and federal spending.

The outcome also will set the tone and political landscape for Obama's expected 2012 re-election bid, which will soon begin in earnest.

In a final pre-election economic snapshot, the government reported that the economy expanded at a 2 per cent annual rate in the July-September quarter. That marked an improvement from the feeble 1.7 per cent growth in the April-June quarter, but the economy still isn't growing at a strong enough pace to make a noticeable dent in the high unemployment rate of just under 10 per cent. Nearly 15 million Americans are out of work.

Obama, speaking at a metal company in Maryland to push one of his job growth proposals, pledged anew to speed up the recovery.

"Political season is going to be over soon," the president said. "And when it does, all of us are going to have a responsibility, Democrats and Republicans, to work together wherever we can to promote jobs and growth."

Such calls for bipartisanship have so far done little. House Republican leader John Boehner, who stands in line to replace Pelosi as speaker, already has ruled out making compromises with Obama.

In the final scramble of the campaign, the politics in Florida grew ever more testy in the three-way Senate race.

The Obama-endorsed last-place candidate, Democrat Kendrick Meek, denied reports that former President Bill Clinton had advised him to drop out. Meek instead pinned the idea on his independent rival, Gov. Charlie Crist, the former Republican who may split votes with Meek. Republican Marco Rubio, who enjoys tea party backing, remains the front-runner in one of the nation's key political states.

Both sides geared up for their final get-out-the-vote pushes in key states. Pelosi, in a fundraising email, said the outcome of many races was too close to determine and "that story will be written in this weekend."

In Washington, Democrats asked congressional staffers to head to West Virginia to help Gov. Joe Manchin win a tight Senate race. Republicans sought volunteers to head to Ohio to help defeat Gov. Ted Strickland.

Republicans also were arming volunteers in Nevada and Colorado this weekend with iPads to collect information in real time from voters as they knocked on some 300,000 doors in each state.

In Virginia, Obama was returning to the state that made him the first Democrat to score a presidential win there since 1964. Perriello won -- barely -- in highly favourable conditions two years ago but is now fighting fiercely to keep the job. His mostly rural, conservative district takes up an enormous triangular swath of central and south Virginia. Obama was seeking to rally younger voters and turn out black supporters in a district that is about one-fourth African-American.

Obama on Saturday will be campaigning in Connecticut, Pennsylvania and Illinois, ending with an evening event in his hometown Chicago in hopes of recapturing some of the magic of his own presidential campaign. His last big event will be Sunday in Ohio before he returns to Washington.