MUNSTER, Ind. (AP) _ Hillary Rodham Clinton called for a vote Friday in the Democratic-controlled Congress on a summertime suspension of the federal gasoline tax, a plan that Barack Obama dismissed as a political stunt that would cost thousands of construction jobs.

"It's a Shell game. Literally," Obama said to laughter from his campaign audience, adding it would mean little for hard-pressed consumers.

The Democratic presidential rivals highlighted their differences in ads and speeches across North Carolina and Indiana, two states with primaries Tuesday.

Polls point toward a particularly close finish in Indiana, which is next door to Obama's home state of Illinois.

Surveys show him with a dwindling advantage in North Carolina, and Clinton decided to spend all of Friday and Saturday in the state before returning to Indiana for a final push. Both candidates addressed the North Carolina Democratic Party's Jefferson-Jackson dinner Friday night.

"North Carolina is going to help elect the next president," Clinton called out to a raucous crowd. About an hour later, Obama told the thousands in attendance, "It starts right here, on Tuesday, right here in North Carolina!"

The two primaries have 187 national convention delegates at stake.

Obama, the front-runner, leads in the overall delegate competition, 1,736.05-1605.5. Clinton won a decisive victory last week in Pennsylvania and is counting on a strong run through the late primaries to persuade convention superdelegates to help her overtake her rival. She picked up the support Friday of Democratic National Committee member Jaime A. Gonzalez Jr., a Texas superdelegate, and two pledged delegates from final results from last week's Pennsylvania primary.

Jolted by Thursday's defection of Joe Andrew, a former national party chairman, Clinton responded with a letter from seven other former party heads and the family of an eighth.

"Her base of support includes women, Hispanics, seniors, Catholics, middle and low-income Americans, and rural, suburban and urban voters. That's a formidable coalition tailor-made for victory in a November general election," they wrote.

They added that if the election were held today, Clinton would defeat Republican Sen. John McCain and win the White House. "Obama would lose to the presumptive GOP nominee," they wrote.

Polls are equivocal on that point. Moreover, they have been particularly volatile in recent weeks as campaign criticism takes its toll on the two Democrats and Obama grapples with controversy stemming from the rhetoric of his former pastor, the Rev. Jeremiah Wright.

Despite a fierce, occasionally personal campaign, to a surprising degree the former first lady and Obama have generally agreed on most policy issues.

That made the proposed suspension in the gasoline tax an exception.

And while there is little support among the Democratic congressional leadership for the plan, it was a disagreement that both presidential contenders appeared content to perpetuate.