(CNN) -- It's all tied up in Texas.

Sens. Hillary Clinton and Barack Obama are running a tight race in Texas.

A new CNN/Opinion Research Corp. poll suggests the battle for the Democratic presidential nomination between Sens. Hillary Clinton of New York and Barack Obama of Illinois is a statistical dead heat in Texas, which holds primaries March 4.

In the survey, out Monday, 50 percent of likely Democratic primary voters support Clinton as their choice for the party's nominee, with 48 percent backing Obama.

But taking into account the poll's sampling error of plus or minus 4½ percentage points for Democratic respondents, the race is a virtual tie. Watch Democrats target Texas. »

Two recent polls by other organizations also show the race statistically even. Map: National and state polling

"One reason the race appears to be tight is that Texas Democrats are having a hard time choosing between two attractive options," says CNN polling director Keating Holland.

"Likely Democratic primary voters would be equally happy if either candidate won the nomination, and they don't see a lot of difference between them on several top issues.

"Roughly a quarter of likely voters say they could change their minds in the next two weeks -- and not surprisingly, those people are splitting roughly equally between Clinton and Obama."

Many political strategists and analysts consider Texas and Ohio -- which also holds a March 4 primary -- must-win states for Clinton. Obama has won the past eight contests and is now ahead in the overall battle for delegates, 193 of which are at stake in Texas.

The new survey indicates Arizona Sen. John McCain is the clear favorite for the Republican presidential nomination.

Among Republicans, 55 percent of likely Texas GOP primary voters support McCain as their choice for nominee. Thirty-two percent back former Arkansas Gov. Mike Huckabee and 11 percent support home-state congressman and former Libertarian standard-bearer Ron Paul. The poll's sampling error for Republican respondents is 4 percentage points.

The CNN/Opinion Research Corp. poll was conducted by telephone from Friday through Sunday. Pollsters talked to 1,506 adults in Texas, including 553 likely Republican primary voters and 529 likely Democratic primary voters.

McCain is the overwhelming front-runner in the fight for the Republican presidential nomination and party leaders have rallied around the candidate in an attempt for party unity.

The poll was released on the same day the only living former Republican president -- George Herbert Walker Bush, the current president's father -- endorsed McCain at an event in Houston. Watch McCain get a big boost »

But McCain has had trouble winning conservative voters. Just last week, McCain lost the conservative vote to Huckabee in the Virginia primary, according to exit polls. The new survey, though, suggests McCain may have better luck in Texas.

"It looks like McCain has made some inroads with conservative Republicans," Holland said.

"McCain is picking up a bare majority among conservative likely voters in the GOP primary. The McCain campaign probably wishes that number were higher, but it does mean that a McCain victory in Texas would not be based on the votes of moderates and independents, as has happened in several states in the past few weeks."

Texas Democrats and Republicans may not see eye to eye on the issues, but the poll suggests they do agree on what's the most important issue. Thirty-five percent of Democrats and an equal number of Republicans said the economy was the most important issue in their choice for president.

The second most important issue for Democrats was health care, at 23 percent, followed by the war in Iraq at 22 percent, illegal immigration at 10 percent and terrorism at 7 percent.

Nineteen percent of Republicans said illegal immigration was their most important issue, putting it in second place, followed by the war in Iraq and terrorism at 17 percent and health care at 8 percent.

Sixty percent of Republicans say they'll definitely support the candidate they are now backing. That number climbs to 76 percent for Democrats.

Likely Democratic primary voters view Clinton and Obama on roughly equal terms. Seventy-nine percent say they would be satisfied if Clinton were the nominee; an equal number feel the same way about Obama. Seventy-nine percent say it's likely Clinton can win the nomination; 82 percent say the same about Obama.

The two candidates are essentially tied on immigration, Iraq and the economy, but Clinton has an advantage on health care and abortion. E-mail to a friend

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