Clinton, in turn, stood by both her comment on Iran and her tax proposal as she gave chase in Indiana and North Carolina to the front-runner for the nomination.

The competitors squabbled over the issues - one foreign, one domestic - from a short distance, first during separate appearances on Sunday news shows and then as they courted voters for Tuesday's primaries.

"This is the final push," Clinton told a cheering crowd of volunteer canvassers in Fort Wayne, emboldened by her Pennsylvania victory two weeks ago as well as polls that show her in a close race in Indiana and narrowing Obama's lead in North Carolina.

A few hours later and a few miles away, Obama urged an audience of several thousand to vote for him. "I need help," he said.

The Illinois senator hopes that wins this week will stop the bleeding from a difficult campaign stretch. Maneuvering for advantage and trying to put the controversy over his former pastor behind him, Obama sought Sunday to portray Clinton as a political opportunist on both Iran and her gas-tax plan.

The two rivals crossed paths at the state Democratic party's Jefferson Jackson Day dinner. Both candidates received loud cheers and applause from their respective supporters.

Clinton pushed her proposal for a summer suspension of the gasoline tax, which she would pay for with a windfall profit tax on oil companies.

"We can't just plan for the future, we have to help people in the here and now," Clinton said. "The choice to me is clear, we need to go after the oil companies."

Obama, who calls the proposal a gimmick, told the same audience that oil companies would "simply jack up their price to fill the gap" if such a gas tax holiday were observed. "Does anybody here really trust the oil companies to give you the savings instead of just pocketing the money themselves?" he asked.

Obama rolled out a new TV ad for Indiana and North Carolina that derided "Clinton gimmicks that help big oil."

Many economists oppose the plan and Clinton, during an interview on ABC's "This Week," demurred when asked to name one who supports it. "I'm not going to put my lot in with economists because I know if we did it right ... it would be implemented effectively," she said.

In a CBS News/New York Times poll released Sunday, 49 percent of voters said they thought lifting the gas tax for the summer was a bad idea. Only 45 percent thought it was a good idea.

Earlier, on NBC's "Meet the Press," Obama seized on an answer Clinton gave recently when asked what she would do if Iran attacked Israel with nuclear weapons on her watch.

"I want the Iranians to know that if I'm the president, we will attack Iran," Clinton said April 22 in an interview with ABC. "In the next 10 years, during which they might foolishly consider launching an attack on Israel, we would be able to totally obliterate them."

Obama said, "It's not the language we need right now, and I think it's language reflective of George Bush" akin to "bluster and saber rattling."

"Senator Clinton during the course of the campaign has said we shouldn't speculate about Iran, we've got to be cautious when we're running for president, she scolded me on a couple of occasions on this issue, yet a few days before an election, she's willing to use that language," Obama added.

Clinton, asked about Obama's criticism, didn't back away from her comment.

"Why would I have any regrets? I'm asked a question about what I would do if Iran attacked our ally ... and, yes, we would have massive retaliation against Iran," Clinton said. "I don't think they will do that, but I sure want to make it abundantly clear to them that they would face a tremendous cost if they did such a thing."

Clinton and Obama both shuffled their schedules to dart back to North Carolina on Monday, reflecting the tightening contest there.

Obama is ahead in the hunt for convention delegates - 1,742.5 to 1,607.5, according to an Associated Press count Sunday - but he has faced a spate of troubles over the past month. That has Clinton sensing an opening. Still, the delegate math works in Obama's favor, and it will be difficult for Clinton to overtake him.

Nevertheless, Clinton suggested anew she had no intention of dropping out, saying on ABC, "When the process finishes in early June, people can look at all the various factors and decide who would be the strongest candidate" to go up against McCain.

Obama told NBC, "We are going to keep on going and we feel confident that I am going to be the Democratic nominee."

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Associated Press Writer Tom Coyne in Fort Wayne, Ind., contributed to this report.

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