BILLINGS — Montana’s Democratic presidential primary is narrowing to a battle over undecided voters, as Hillary Rodham Clinton and Barack Obama look to persuade last-minute fence-sitters to back their campaigns.

A recent poll by Lee Newspapers showed Obama with a 17-point lead over Clinton among likely Democratic voters in Montana, although 13 percent said they were still undecided. Political experts say Clinton has a lot of ground to cover — both in Montana and nationally, where she trails Obama in total delegates.

A loss in the June 3 primaries in Montana and South Dakota — the last two contests in the nation — could derail Clinton’s strategy of wooing superdelegates by portraying herself as the best candidate to beat Republican Sen. John McCain in the fall.

“If you add all the undecideds to her column, then you’ve got something approximating a dead tie in Montana,” said Kenneth Bickers, a University of Colorado political analyst who has been tracking the race. “And at this point, she can’t just tie. She has to beat him.”

Both campaigns say they are reaching out to undecided voters, knocking on doors and making phone calls. Candidate visits are also key. Clinton was in Montana on Tuesday, holding a town hall meeting on the Flathead Indian Reservation. An evening rally was planned in Billings.

Clinton has triumphed over ominous poll numbers before. Capturing large percentages of previously undecided voters helped the New York senator secure victories in Pennsylvania, New Hampshire, West Virginia and Kentucky, Bickers said.

But her recent string of “moral victories,” as Bickers called them, have not been enough to overcome a delegate count tilting increasingly in Obama’s favor.

As of Tuesday, the Illinois senator was within 48 delegates of the 2,026 needed to win the Democratic nomination.

Thirty-one pledged delegates are at stake in Montana and South Dakota plus the potential support of the state’s superdelegates — elected officials and party leaders who can vote for whomever they choose at the Democratic national convention in August.

In Montana, undecided superdelegates include Gov. Brian Schweitzer and U.S. Sens. Max Baucus and Jon Tester.

Clinton spokeswoman Kate Downen said the large percentage of undecided voters showed there was still room for victory and the campaign planned various outreach efforts.

Obama spokesman Matt Chandler said their campaign will also compete for those undecided voters.

“We expect this to be a close contest, most likely a difference of only single digits,” Chandler said.

Bickers said the large proportion of undecided voters leading up to the final primaries could signal a fundamental weakness for Obama: an inability to reach beyond a core group of passionate supporters.

“Typically, people want to get behind a winner,” Bickers said. “He’s got a bare majority that are willing to support him in the primary, when (the nomination) is essentially wrapped up at this point. That’s a sign of a weak nominee.”

James Lopach, chair of University of Montana’s political science department, said many of the undecided voters were unlikely to cast ballots on June 3 since they have yet to be swayed by either candidate.

He also said Clinton needs more than just wins in Montana and South Dakota, given Obama will still pick up delegates even if he loses because Democrats use a proportional system rather than winner-take-all.

“(Clinton) needs some kind of a horror story regarding Obama that’s going to make superdelegates change their minds,” Lopach said.