barack_obama_5.jpgWASHINGTON (AP) _ Barack Obama appears to be on the verge of becoming the first black presidential nominee of a major U.S. political party.

The Illinois senator is a little more than 30 short of the 2,118 needed to win the nomination. Aides predicted the first-term senator could clinch the nomination as early as this week, as Montana and South Dakota close out a bitter and hard-fought primary season on Tuesday.

Obama’s rival, Sen. Hillary Rodham Clinton, entered this week with an insurgent strategy not only to win over undecided superdelegates but to peel away Obama's support from those party leaders and elected officials who already have committed to back him for the nomination.

“One thing about superdelegates is that they can change their minds,'' she told reporters aboard her campaign plane Sunday night.

Obama displays no signs of worry, pivoting toward the November general election against presumptive Republican presidential nominee John McCain. Some of Clinton's own backers are saying the time is near for her to fall in behind Obama.

Clinton won a lopsided but largely symbolic victory Sunday in Puerto Rico _ a Caribbean U.S. territory that votes in the primaries but does not participate in the presidential general election. She won 38 delegates and Obama gained 17.

With 31 delegates at stake Tuesday, Obama could close the gap further and cue undecided superdelegates to come to his side.

Obama is favored in both South Dakota and Montana.

U.S. Rep. James E. Clyburn of South Carolina, the highest-ranking African American in the House leadership, announced his support for Obama on Tuesday. Others, including Sens. Max Baucus and Jon Tester of Montana, indicated that they would endorse Obama after the votes come in from their state, according to published reports.

Obama, campaigning in Mitchell, South Dakota, confidently predicted Clinton “is going to be a great asset when we go into November.''

“Whatever differences Senator Clinton and I may have, those differences pale in comparison to the other side,'' he said.

The Illinois senator has made up most of the ground he lost Saturday when the national party's rules committee agreed to reinstate delegates from Michigan and Florida. The party had initially refused to seat the delegates as punishment for scheduling their contests in violation of party rules.

But Clinton argues she now leads in the popular vote _ a debatable point given that she relies on Michigan and Florida outcomes. None of the candidates campaigned in either state and Obama received no votes in Michigan because he removed his name from the ballot. Clinton also continues to present herself as better able to confront McCain in the fall.

She and her campaign's national chairman, Terry McAuliffe, both made it clear Sunday night that Obama's supporters were now fair to pluck with those arguments.

To drive the point home, Clinton invited Virgin Islands superdelegate Kevin Rodriguez, a recent convert, to travel with her to South Dakota on Monday. Rodriguez had initially supported Clinton, switched to Obama, and recently returned to the New York senator's camp.

“This has been such an intense process,'' Clinton said, “I don't think there has been a lot of time for reflection. It's only now that we're finishing these contests that people are going to actually reflect on who is our stronger candidate.''

Her decision, if prolonged, is not likely to sit well with party leaders and some of her own supporters. Democrats House Speaker Nancy Pelosi and Senate Majority Leader Harry Reid have both called on the contest to end shortly after the final primaries.

Tom Vilsack, the former Iowa governor and a national co-chairman of Clinton's campaign, said Sunday: “It does appear to be pretty clear that Senator Obama is going to be the nominee. After Tuesday's contests, she needs to acknowledge that he's going to be the nominee and quickly get behind him.''

Meanwhile, Clinton said she was still contemplating whether to challenge the decision by the Democratic Party's rules committee to split the Michigan delegates 69-59 in her favor. Each delegate would have a half vote. The agreement granted Obama 55 uncommitted Michigan delegates and four who would have been assigned to Clinton based on the state's results.