WASHINGTON (Reuters) - Hillary Clinton and rival Barack Obama are running neck-and-neck in Ohio and Texas one day before their crucial Democratic presidential showdowns, according to a Reuters/C-SPAN/Houston Chronicle poll released on Monday.

Clinton, fighting to save her presidential bid after 11 straight wins by Obama, desperately needs victories in the big-state battles to keep her candidacy alive and face the Republican candidate in the November election.

Obama, an Illinois senator, has a slim advantage on Clinton in both states, although the leads are within the poll’s margin of error of just under 4 percentage points.

Obama leads 47 percent to 44 percent in Texas, as Clinton gained 1 point overnight in the polling conducted by Zogby International. He leads 47 percent to 45 percent in Ohio, a turnaround from Clinton’s 1-point advantage on Sunday.

Obama has wiped out big leads in the last two weeks in both states for Clinton, a New York senator and former first lady, but in the final days of the race neither candidate has managed dramatic shifts.

“There are no big movements, no great swings, these are just very tight races,” pollster John Zogby said. “At least for now it doesn’t look like either one of them is going to be winning in a blow-out.”

Republican front-runner McCain, however, appears headed to easy victories in both states. He has big double-digit leads over his last major rival, former Arkansas Gov. Mike Huckabee.

McCain, an Arizona senator, is moving closer to clinching the Republican presidential nomination and has built an insurmountable lead in delegates, who will choose the nominee at the party’s September convention.

COALITIONS STABLE

Both Democratic candidates have maintained the voter coalitions in Ohio and Texas that fueled them in earlier contests, with Clinton winning women, older voters, traditional Democrats and Hispanics while Obama attracts men, young voters, blacks and independents.

In Texas, Clinton continues to hold a big lead among the state’s sizable bloc of Hispanics and has an edge in the state’s heavily Hispanic south and conservative west. Obama is strong in the cities, but the two have battled back-and-forth in east Texas and now run even there.

“It really is looking like east Texas is the place to watch in the popular vote, whoever wins there could have the edge in the state,” Zogby said.

Clinton moved ahead slightly in Ohio among voters who made their decision in the last few days -- a possible sign Obama’s momentum could be slowing after days of Clinton attacks on his readiness to become U.S. commander-in-chief.

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In Ohio and Texas, 6 percent of Democrats are still undecided on the day before the primary.

In the Republican race, McCain leads Huckabee 61 percent to 28 percent in Ohio and 53 percent to 33 percent in Texas. The other remaining Republican candidate, Texas Rep. Ron Paul, had 6 percent in Texas and 5 percent in Ohio.

McCain leads handily in nearly every voter category and in all regions of both states. He even leads in Ohio among those who call themselves very conservative, although Huckabee leads in that category in Texas.

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McCain has faced a revolt among some conservatives unhappy with his past stances on immigration, tax cuts and campaign finance reform, although it has done little to slow his march to the nomination.

The rolling poll was conducted Friday through Sunday. It surveyed 761 likely Democratic voters in Ohio with a margin of error of 3.6 percentage points, and 748 in Texas with a margin of error of 3.7 percentage points.

The poll of 675 likely Republican voters in Ohio had a margin of error of 3.9 percentage points. The survey of 628 voters in Texas had a margin of error of 4 percentage points.

In a rolling poll, the most recent day’s results are added and the oldest day’s results are dropped to track changing momentum. The poll will continue one more day.

(Editing by Jackie Frank)