Illinois Sen. Barack Obama failed to deliver a knock-out blow to New York Sen. Hillary Rodham Clinton on Tuesday night, increasing the likelihood that an Obama-Clinton race will still be going strong by the time North Carolina's presidential primary is held May 6.

North Carolina is the second-richest prize remaining before Democrats gather at their national convention Aug. 25 through 28 in Denver to choose their nominee. North Carolina has 134 delegates. Pennsylvania, which holds its primary April 22, has 188.

With Clinton's victories in Texas, Ohio and Rhode Island, it's becoming more likely -- although it's not a certainty -- that she and Obama will wage a full-scale campaign here, complete with numerous appearances, TV and radio ads, and the attention of the national media. It is a familiar snowy scene in such early states as Iowa and New Hampshire but a rare Southern spring tableau.

"She can certainly say that she has made it close enough tonight that she can go on to Pennsylvania," said Peter Francia, a political science professor at East Carolina University "If she holds her lead in Pennsylvania, then certainly we've got one heckuva race in North Carolina."

For the Republicans, however, the contest is over, with Arizona Sen. John McCain winning the nomination Tuesday.

A full-fledged Obama-Clinton race could change the chemistry of North Carolina's other Democratic primaries, including contests for governor, the U.S. Senate, Council of State and the legislature.

If other state primaries are any guide, North Carolina will likely see a surge in voter interest, particularly among African-Americans, young voters and unaffiliated voters, who are allowed to vote in Democratic or Republican primaries.

Obama would likely have a built-in advantage in North Carolina, in part because of state's sizable African-American population. In a Democratic primary, black voters typically make up just under 30 percent -- although that could go as high as 35 percent in a race involving Obama, the first serious African-American presidential candidate.

A recent statewide poll conducted for the Civitas Institute, a conservative think tank in Raleigh, found Obama leading Clinton in North Carolina, 38 percent to 24 percent, with 38 percent undecided.

Many of North Carolina's delegates are awarded by congressional districts. Obama might do well in districts with sizeable African-American populations and more liberal-leaning urban areas such as the Triangle. Clinton might do better in more white, rural districts.

"Obama is likely to do well in urban communities, in Durham County and places like that," Francia said. "What is interesting is where rural America will go. On Super Tuesday, Hillary Clinton won the rural areas. But if you look at the rural vote in South Carolina and Virginia, Barack Obama won there. That vote is very much for grabs."

A continued Obama-Clinton race is likely to put pressure on North Carolina's top elected leaders, including the superdelegates, to endorse either Obama or Clinton in a primary.

A coalition of voters based in Chapel Hill called Voters for Obama announced Tuesday that it was undertaking a petition drive to pressure superdelegates including U.S. Reps. David Price and Brad Miller and Gov. Mike Easley to back Obama.

Former Sen. John Edwards, who suspended his presidential campaign in January, would be under pressure to endorse. Both Clinton and Obama have visited him in his home outside Chapel Hill.

A competitive presidential race could also have an important impact on North Carolina races, by producing a wave of new voters excited by the presidential campaign.

The conventional wisdom is that a high turnout could benefit Lt. Gov. Beverly Perdue in her Democratic primary for governor with state Treasurer Richard Moore. Perdue is leading in the polls primarily because of her strong support among women and African-Americans -- two groups likely to show up in big numbers.

Moore has sought to counter this by backing Obama. He is the only major statewide official to endorse.

North Carolina has not been a player in primary politics since 1988, when the state was part of the Democrats' first Super Tuesday -- a group of Southern states that banded together to play a larger role in the presidential states. North Carolina voted for Tennessee Sen. Al Gore that year, but state voters ultimately had little effect. Massachusetts Gov. Michael Dukakis won the nomination.