WASHINGTON (Reuters) - Democratic presidential hopeful Barack Obama surged to a big lead over Hillary Clinton in California hours before “Super Tuesday” voting began in 24 states, according to a Reuters/C-SPAN/Zogby poll released on Tuesday.

In the Republican race, former Massachusetts Gov. Mitt Romney held a 7-point advantage on Arizona Sen. John McCain in California, while McCain added to commanding double-digit leads in New York and New Jersey.

On a sprawling day of coast-to-coast voting, the biggest ever in a U.S. primary race, the U.S. presidential contenders in both parties were fighting to win a huge cache of delegates to this summer’s nominating conventions.

In California, which alone provides more than one-fifth of the Democratic delegates needed for the nomination, Obama led Clinton by 49 percent to 36 percent, the poll found. The margin of error was 3.3 percentage points.

Clinton pulled into a 5-point lead in New Jersey, 46 percent to 41 percent, after being tied on Monday. Obama held a 45 percent to 42 percent edge on Clinton in Missouri. Both polls had a margin of error of 3.4 percentage points.

Obama had a 20-point edge in Georgia, aided by a more than 3-to-1 lead among black voters.

Obama, an Illinois senator, and Clinton, a New York senator, are in a hard-fought battle for the Democratic presidential nomination and split the first four significant contests.

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“There is clear Obama momentum in California,” pollster John Zogby said. “But in New Jersey, things seemed to swing in favor of Clinton, and Missouri was very mixed.”

In the Republican race, Romney maintained a stable 40 percent to 33 percent lead on McCain in California, fueled by heavy support in the southern part of the state and among self-described conservatives. The margin of error was 3.4 percentage points.

DASH TO CALIFORNIA

Both Romney and McCain made last-minute changes to their campaign schedules to fly to California for late appearances. A Romney win there could be his last hope of blunting McCain’s growing momentum in other states.

McCain held a 26-point edge on Romney in New York and a 29-point advantage in New Jersey as he pushed for a convincing triumph that could knock Romney out of the race to be the Republican candidate in November’s presidential election.

McCain held a narrow 34 percent to 27 percent lead over former Arkansas Gov. Mike Huckabee in Missouri, with Romney running third at 25 percent. The margin of error was 3.4 percentage points.

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“It looks like a big day for McCain with Romney making a last stand in California,” Zogby said.

The two launched hard-hitting attack ads on Monday questioning each other’s conservative credentials before the vote.

McCain won the last two contests, in South Carolina and Florida, to seize the front-runner’s slot in a hard-fought Republican race despite qualms among some conservatives about his views on taxes, immigration and campaign finance.

More than half of the total Democratic delegates and about 40 percent of the Republican delegates are up for grabs on Tuesday.

The Reuters/C-SPAN/Zogby rolling tracking poll surveyed presidential races in both parties in California, New Jersey and Missouri. The polls also looked at the Republican race in New York and the Democratic race in Georgia.

The rolling polls were taken Saturday through Monday, except for the California survey, which was a two-day poll on Sunday and Monday. In a rolling poll, the most recent day’s results are added while the oldest day’s results are dropped in order to track changing momentum.

(Editing by Patricia Zengerle)