By David Morgan

WASHINGTON (Reuters) - Democratic presidential candidate Hillary Clinton warned Tehran on Tuesday that if she were president, the United States could "totally obliterate" Iran in retaliation for a nuclear strike against Israel.

On the day of a crucial vote in her nomination battle against fellow Democrat Barack Obama, the New York senator said she wanted to make clear to Tehran what she was prepared to do as president in hopes that this warning would deter any Iranian nuclear attack against the Jewish state.

"I want the Iranians to know that if I'm the president, we will attack Iran (if it attacks Israel)," Clinton said in an interview on ABC's "Good Morning America."

"In the next 10 years, during which they might foolishly consider launching an attack on Israel, we would be able to totally obliterate them," she said.

"That's a terrible thing to say but those people who run Iran need to understand that because that perhaps will deter them from doing something that would be reckless, foolish and tragic," Clinton said.

Her comments appeared harder than a week ago, when during a presidential debate she promised "massive retaliation" against any Iranian attack on Israel.

Obama rejected Clinton's rhetoric as saber rattling on a day when Pennsylvania Democrats voted in a party primary contest that could help decide which Democrat will face Republican John McCain for the White House in the November general election.

"One of the things that we've seen over the last several years is a bunch of talk using words like 'obliterate,"' Obama, an Illinois senator, said in a separate ABC interview. "It doesn't actually produce good results. And so I'm not interested in saber rattling."

CONTRADICTION ACCUSATION

The Obama campaign also issued a statement saying Clinton was contradicting her remarks at an August debate, where Obama spoke in favor of taking unilateral military action in Pakistan if the United States had actionable intelligence on the whereabouts of senior al Qaeda members.

Clinton had said she did not believe "people running for president should engage in hypotheticals" and called it a mistake "to telegraph" what U.S. strategy might be at a time of unrest inside Pakistan.

At a Tuesday news conference in the Philadelphia suburb of Conshohocken, Pennsylvania, Clinton said the question of Iran merited hypothetical discussion because a nuclear Tehran would require straightforward Cold War-style deterrence. "It's a question not of what might be on or off the table," she said.

Meanwhile, Obama said he would respond "forcefully and swiftly" to an Iranian attack against Israel or any other U.S. ally, whether conventional or nuclear.

Iran, which Washington and its allies charge is seeking nuclear arms, has voiced war-like rhetoric in recent years amid speculation its nuclear facilities could face U.S. or Israeli military action.

Tehran denies it is trying to acquire nuclear weapons and says it needs nuclear technology to generate electricity.

Israel is widely believed to have nuclear weapons but, as part of a policy of "strategic ambiguity," has not confirmed or denied the nature of its arsenal.

Iranian President Mahmoud Ahmadinejad outraged the international community in 2005 by saying "Israel should be wiped off the map." A week ago, a senior Iranian army commander said Iran would "eliminate" Israel in response to any military attack from the Jewish state.

(Additional reporting by Jeff Mason in Conshohocken; Editing by Eric Walsh and Bill Trott)