(CNN) -- Sens. Hillary Clinton and Barack Obama are in a statistical dead heat in Texas, according to a poll released eight days before the state's crucial presidential primary.

Sen. Barack Obama has won the past 11 contests and leads in the overall delegate count.

In the CNN/Opinion Research Corp. survey released Monday, 50 percent of likely Democratic primary voters said Obama is their choice for the party's nominee, while 46 percent backed Clinton.

But taking into account the poll's sampling error of plus or minus 3.5 percentage points for Democratic respondents, the race is a virtual tie.

Clinton had a statistically insignificant 50 percent to 48 percent edge over Obama in last Monday's CNN/ORC poll in Texas.

"The 2-point gain for Obama and the 4-point drop for Clinton are both within the poll's sampling error, so although the survey appears to indicate some movement toward Obama, we cannot say for certain that he has gained any ground since last week," said CNN polling director Keating Holland.

Two recent polls by other organizations also show the race statistically even.

Texas and Ohio, which both hold primaries March 4, are considered must-win states for Clinton. Watch what challenges the candidates face in Texas, Ohio »

Obama has won the past 11 contests and is ahead in the overall battle for delegates, 193 of which are at stake in Texas.

The new survey indicates John McCain is the clear favorite in Texas for the Republican presidential nomination. Among likely Republican primary voters, 56 percent said the senator from Arizona is their choice for nominee.

Former Arkansas Gov. Mike Huckabee won the backing of 31 percent of those questioned, and Rep. Ron Paul of Texas was at 9 percent. These numbers are virtually unchanged from last week's poll. The survey's sampling error for Republican respondents is also plus or minus 3.5 percentage points.

McCain is the overwhelming front-runner in the fight for the GOP presidential nomination and party leaders have rallied around the candidate in an attempt for party unity. Regardless, Huckabee and Paul remain in the race for now.

There are 137 Republican delegates at stake in Texas.

The poll was conducted by telephone from Friday through Sunday. Pollsters talked to 2,149 adults in Texas, including 861 likely Democratic primary voter and 751 likely Republican primary voters.

A breakdown of how whites, African-Americans and Latinos are planning to vote shows one reason the race in Texas between Clinton and Obama is so close.

"Obama appears to be picking up support from nearly eight in 10 blacks," Holland said. "Clinton may win roughly two-thirds of the Latino vote. There are likely to be more Latino voters than blacks when Democrats go to the polls on March 4, which should work to Clinton's advantage.

"But Obama's huge lead among blacks -- plus a noticeable chunk of the Latino vote -- tends to counteract that. The result: Clinton and Obama get roughly equal number of votes from nonwhite Democrats. And since whites appear to be splitting almost evenly between the two candidates, the overall race is a virtual tie."

Clinton and Obama faced off last Thursday at a presidential debate in Austin, Texas, hosted by CNN and the Spanish-language network Univision. The poll suggests the debate gave Obama a boost. Watch how the debate affected poll numbers »

"Among the one-third of Texas Democratic primary voters who watched all or most of the debate, Obama leads Clinton by 20 points," said CNN senior political analyst Bill Schneider.

"Among the 42 percent who followed news about the debate, Clinton and Obama are neck and neck. And among the one-quarter of Texas Democrats who paid no attention to the debate, Clinton leads Obama by nearly 20 points.

"Is this because Obama appeals to better-educated Democrats and they were more likely to watch the debate? No. Even among college-educated Democrats, the more attention you paid to the debate, the better Obama does."

Democrats and Republicans may not agree on the issues, but the poll indicates they do agree on what's the most important issue. Forty-three percent of Democrats and 31 percent of Republicans say the economy is the most important issue in their choice for president.

The second most important issue for Democrats was health care, followed by the war in Iraq, illegal immigration and terrorism. For Republicans, illegal immigration was second, trailed by terrorism, health care and the war in Iraq.

"Likely Democratic primary voters think that Clinton would handle the economy and health care better than Obama," Holland said, "and those are the top two issues on the minds of Democratic voters. Obama has an advantage over Clinton on Iraq."

The candidates and their surrogates are stumping heavily in both Texas and Ohio and both campaigns are advertising extensively. Seeing less traffic are Rhode Island and Vermont, which also hold primaries on March 4. E-mail to a friend

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