Barack Obama likened Hillary Rodham Clinton to President Bush for threatening to "totally obliterate" Iran if it attacks Israel and called her gas-tax holiday a gimmick as he tried to fend off her challenge ahead of two pivotal Democratic primaries.

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 tomorrow'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 yesterday 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.

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 yesterday, 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.