Democratic presidential candidate Hillary Clinton on Sunday dismissed the "elite opinion" of economists who criticised her gas tax proposal, using a term that has dogged rival Barack Obama in recent weeks.

Obama, meanwhile, accused the New York senator of pandering on gas taxes and sabre rattling toward Iran as both candidates gave television interviews before primary contests in North Carolina and Indiana. The two are battling to be their party's nominee and face Republican John McCain in November.

Clinton used her appearance on ABC's This Week to raise questions about Obama's ability to connect with working-class Americans while dismissing economists who have said her plan to suspend gas taxes over the summer would do little good.

"I'm not going to put my lot in with economists," Clinton said when asked to name an economist who backed her proposal.

"We've got to get out of this mind-set where somehow elite opinion is always on the side of doing things that really disadvantage the vast majority of Americans," said Clinton, a former first lady who would be the first woman president.

Critics have painted Obama as elitist for a comment he made about job losses causing some small-town Americans to become bitter and to cling to guns and religion.

That perception hurt the Illinois senator in the big blue-collar state of Pennsylvania, where Clinton won a crucial victory last month in the protracted Democratic contest.

The two candidates next square off in North Carolina and Indiana on Tuesday.

In an interview on NBC's Meet the Press, Obama dismissed Clinton's gas-tax proposal as "a classic Washington gimmick" that has no chance of becoming law.

"What this is is a strategy to get through the next election," he said.

Obama acknowledged he should have more quickly distanced himself from his former pastor, the Reverend Jeremiah Wright, who has suggested the US government created AIDS to kill blacks and the September 11 attacks were payback for US foreign policy.

He did not repudiate Wright completely until last week, after the Chicago preacher reiterated his views.

"When you're in national politics, it's always good to pull the Band-aid off quick," Obama said. "But life's messy sometimes, it's not always neat, and things don't always proceed in textbook Political 101 fashion."

The Illinois senator also compared Clinton's views on Iran to those of unpopular Republican President George W Bush. Clinton has threatened to "totally obliterate" Iran if it attacked Israel.

"It is important that we use language that sends a signal to the world community that we're shifting from the sort of cowboy diplomacy, or lack of diplomacy, that we've seen out of George Bush," he said.

Obama launched a new ad slamming Clinton's gas tax plan.

"Clinton aides admit it won't do much for you, but would help her politically," the ad's announcer says.

Clinton aides said the spot was misleading because a person cited in the Obama ad was actually criticising McCain, not Clinton.

Obama remains the front-runner in the Democratic race, though he is not expected to win enough delegates from state contests to clinch the nomination outright. The nominee is likely to be determined by party insiders.

Opinion polls show Obama losing ground to Clinton in Indiana and North Carolina during the past several weeks.

Obama now leads Clinton by an average of 7 points in North Carolina and trails her by an average of 6 points in Indiana.

Obama spent the afternoon campaigning door-to-door in Elkhart, Indiana, where much of the talk was about high gas prices. One woman said it cost $4 to mow her lawn.

Clinton, meanwhile, encouraged supporters in Fort Wayne, Indiana, to help get people to the polls on Tuesday.

She has spent $US6.7 million in the two states, according to her campaign aides, while Obama has spent $US10.5 million.

On Saturday night, Obama eked out a narrow seven-vote victory in the US Pacific island territory of Guam.