A disagreement over foreign policy in the U.S. presidential election campaign has escalated into the sharpest exchange yet between Democratic contenders Hillary Clinton and Barack Obama.  VOA National correspondent Jim Malone has more from Washington.

The testy exchange began in the recent Democratic candidates debate in South Carolina when Senator Obama was asked if he would meet separately with the leaders of Iran, North Korea, Venezuela and other U.S. adversaries if he were elected president.

Obama said that he would.

"The notion that somehow not talking to countries is punishment to them, which has been the guiding diplomatic principle of this administration, is ridiculous," he said.

In her response, Senator Clinton said that although she supported a renewed emphasis on diplomacy to deal with governments hostile to the U.S., she would not guarantee meetings with those foreign leaders in the first year of her presidency.

"Because I do not think you promise a meeting at that high a level before you know what the intentions are," she said.  "I do not want to be used for propaganda purposes.  I do not want to make a situation even worse."

Later, Clinton suggested Obama was naïve and showed his inexperience by saying he would agree to meet with foreign leaders hostile to the U.S.

Obama fired back, saying Clinton was the one who was irresponsible and naïve by initially supporting President Bush's decision to use military force in Iraq.

"I do not want a continuation of Bush-Cheney!  I do not want Bush-Cheney lite," he said.  "I want a fundamental change."

Clinton told the Cable News Network that the dispute with Obama was becoming, in her words," kind of silly."

"I have been called a lot of things in my life, but I have never been called George Bush or Dick Cheney, certainly," she said.  "You know you have to ask, whatever happened to the politics of hope?"

Political experts say the incident is an example of both candidates trying to play to their strengths, Clinton's experience versus Obama casting himself as an agent of political change.

"You have here the classic defining dynamic between these two candidates.  You have experience on one side and change on the other. The question is, how much change do Democrats want?" said Richard Wolffe, White House correspondent for Newsweek magazine and a guest on this week's Issues in the News program on VOA.

Among Democratic voters, Clinton leads Obama in the latest Washington Post-ABC News poll by a margin of 45 - 30 percent, with six other contenders trailing behind.