WASHINGTON (CNN) -- Democratic Sen. Hillary Clinton is losing ground to Sen. Barack Obama in a national CNN/Opinion Research Corp. poll released on the eve of critical Super Tuesday presidential primaries and caucuses.

The two are virtually tied in Monday's survey, which shows the New York senator has lost a comfortable national lead she's held for months over Obama and other rivals.

The survey also shows Arizona Sen. John McCain as the clear Republican front-runner.

Obama, who trounced Clinton in January's South Carolina primary, garnered 49 percent of registered Democrats in Monday's poll, while Clinton trailed by just three points, a gap well within the survey's 4.5 percentage point margin of error. View the poll results »

"Coming out of his overwhelming victory in South Carolina and followed quickly by his Kennedy family endorsements, Obama clearly has the momentum in this campaign," said Bill Schneider, CNN's senior political analyst.

Obama has won support from Sen. Edward Kennedy and his nieces Caroline Kennedy Schlossberg and Maria Shriver, although Clinton has endorsements from former Maryland Lt. Gov. Kathleen Kennedy Townsend, the daughter of Robert Kennedy, and her brother Bobby Kennedy and sister Kerry. Watch ex-candidate on what he wants from Clinton, Obama »

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The poll is consistent with other national surveys during the past few days. A CNN averaging of five national polls conducted in the last few days -- a "poll of polls" -- puts Clinton at 45 percent and Obama at 43 percent. Those five surveys were done by CNN/Opinion Research Corp., Gallup, Pew, ABC and CBS. Watch what voters are looking for in a candidate »

In the battle for the GOP nomination, McCain has the backing of 44 percent of registered Republicans, while former Massachusetts Gov. Mitt Romney received 29 percent, former Arkansas Gov. Mike Huckabee got 18 percent and Rep. Ron Paul of Texas won 6 percent.

McCain took the top spot in most national surveys of Republican voters after his January 8 victory in the New Hampshire primary.

Prior to that, former New York City Mayor Rudy Giuliani had the lead in the national polls. Giuliani gave up his bid for the White House last week after a third-place finish in Florida's primary.

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CNN's "poll of polls" of the Republican race puts McCain at 45 percent compared with 24 percent for Romney.

"McCain is clearly the front-runner nationwide, thanks in part to his recent victories in South Carolina and Florida. Both McCain and Obama are on the rise not only because they've won important primary victories but because they've captured the change issue. Clinton and Romney tried to echo the change theme but don't appear to have had much success," Schneider said.

The economy remains the top issue on the minds of Americans, according to the new poll. Two-thirds of those questioned say that the economy is in a recession. That's up five points from January and 20 points from October.

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The economy ranked as the most important issue to 44 percent of those surveyed, while 20 percent cited the war in Iraq and 16 percent identified health care. Illegal immigration was the most important issue to 10 percent of respondents, while 8 percent cited terrorism.

"Clinton has an advantage among registered Democrats on most issues, including the economy and health care, but Obama is seen as the candidate who would best handle Iraq," said Keating Holland, CNN's polling director. Watch campaign in one battleground state »

"Republicans nationwide see McCain as best able to handle Iraq and terrorism but view Romney as the candidate most likely to handle the economy," he said. "Mike Huckabee is seen as the GOP candidate who would best handle abortion."

The poll results come out one day before Super Tuesday, which is as close as the country comes to a national primary, as contests will be held 24 states and American Samoa.

The Democratic candidates will compete for 1,681 Democratic delegates Tuesday, less than 400 shy of the 2,025 needed to clinch the nomination. On the Republican side, 1,020 delegates are at stake, just shy of the 1,191 needed to lock up the GOP nomination. See what is at stake on Super Tuesday »

National polls may not be the best indicator of what could happen on Super Tuesday. A look at polls in the crucial states voting Tuesday could give a clearer indication of what may occur.

In the Democratic race, two new polls in California have Clinton up by single digits. New surveys suggest the race is virtually tied in Arizona and Missouri. Clinton leads in Connecticut and New Jersey and is ahead by double digits in her home state of New York. Obama leads in Georgia and is the clear front-runner in his home state of Illinois. Watch how the race is stacking up in California »

McCain has a single-digit lead in California over Romney. That could be one reason why Romney has added a last-minute campaign stop in California on Monday. Polls suggest McCain has large leads in New York, New Jersey, Connecticut and Illinois, but he's only ahead by single digits in Georgia and Missouri. Watch Romney respond to McCain's criticism »

The key to many races are undecided voters, which could make up from 10 to 15 percent of those who cast ballots.

There is one thing Democrats and Republicans agree upon, according to the poll, 58 percent of registered Democrats and 56 percent of registered Republicans say clear winners won't emerge from Super Tuesday.

Looking ahead to the general election in November, Clinton tops McCain 50 percent to 47 percent and beats Romney 56 to 41 in hypothetical matchups. Obama beats McCain 52 percent to 44 percent and tops Romney 59 percent to 36 percent.

"Issues also appear to play a big role as registered voters nationwide look ahead to general elections matchups," Holland said.

"Will the race boil down to a fight over foreign policy, or will 2008 be the year of 'It's the Economy, Stupid -- the Sequel'? If it's foreign policy, McCain has the edge -- he is seen as better able to handle Iraq and terrorism than Clinton or Obama. If it's the economy, which is the top issue with voters, the Democrats have an advantage; either Clinton or Obama is seen as better able to handle the economy than McCain," Keating said.

The poll surveyed 1,192 adults. Of 974 registered voters, 500 described themselves as Democrats and 412 identified themselves as Republicans.

The poll was conducted by telephone from February 1-3, 2008. E-mail to a friend

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