Harrisburg, Pennsylvania  - Supporters of Democratic presidential hopefuls Hillary Clinton and Barack Obama have always been adamant about their chosen candidates, but as the battle for the party's nomination drags on they are digging even deeper into their trenches.

Clinton won a key victory in the eastern state of Pennsylvania on Tuesday, prolonging the state-by-state nominating process that has narrowed the contest to two candidates locked in a a near dead heat.

Ahead of Pennsylvania, Obama had a small but significant lead in the number of delegates needed to secure the nomination at the party convention in August, but neither candidate has been able to come close to the 2,024 delegates needed.

Early in the campaign, voters preferred one candidate over the other, but frequently said they would be happy to have either Democrat represent them in November. But months later, voters seem less likely to yield their candidate's ground.

At an Obama rally in February, Bruce Danver, a 48-year-old engineer, said he would support either Democrat in the general election but sounded an ominous warning.

"This could be protracted. It could get ugly," he said.

His words seem prophetic after a series of barbed ad campaigns and controversies.

"We would show a little bit of weakness towards the Republicans," Franklin Sejas, a 34-year-old Clinton supporter, said this winter of the consequences of a drawn-out race. "You have to be a decider. You've got to know what you want."

But those who have not grown weary of the wall-to-wall media coverage are no closer to moving the party toward a definitive decision and instead are more entrenched than ever behind their favourite candidate.

"I want Hillary to win. I may end up voting for Obama in the general election, but I don't think he tells a lot about what he's going to do," Carol Komesz, 60, said at a Clinton rally in Harrisburg ahead of Pennsylvania's vote.

Interviews conducted by CNN of voters leaving the polls showed nearly one-third of voters in Pennsylvania would be satisfied only if Clinton wins the nomination, 23 per cent would only be satisfied with Obama as the nominee, and only 40 per cent would be happy with either candidate.

In contrast, in Virginia's February vote, just 15 per cent said they would be satisfied only if Clinton wins the nomination, 34 per cent said they would be happy only with an Obama win and 48 per cent would take either outcome.

In the heat of the ongoing battle, voters seem less willing to yield ground to the other candidate.

Some staunch Clinton supporters, like Dana Thompson, 39, of York, Pennsylvania, think the senator from neighbouring New York should stay in the race no matter what.

"It makes me crazy when people say she needs to drop out. She's not that far behind - they're neck and neck," she said before a Clinton rally on Monday. "Why should she step aside? Women have historically stepped aside." (dpa)