(Adds Gates comment)

By Caren Bohan

WASHINGTON, May 20 (Reuters) - Ronald Reagan met Mikhail Gorbachev, Richard Nixon met Mao Zedong and John F. Kennedy met Nikita Khrushchev, so why shouldn't the next U.S. president meet with Mahmoud Ahmadinejad?

Democrat Barack Obama says he is willing to sit down with the Iranian leader. Republican John McCain calls that "reckless."

The two have sparred over whether U.S. presidents should meet with adversaries -- despite Washington's long history of doing so -- in a clash that could help define the foreign policy debate ahead of the November presidential election.

McCain, an Arizona senator and Vietnam War hero, has hammered Obama daily on the issue, suggesting he sees a chance to paint him as soft on national security.

But several analysts said the strategy may not work. Fatigue with the Iraq war may make Americans more open to the the likely Democratic nominee's call for stressing diplomacy.

"The Cold War rhetoric and even the terrorism rhetoric are becoming old hat," said Stephen Wayne, a professor of government at Georgetown University. "The mood of the American public seems to be one where there is a sense that talking is probably better than fighting."

James Lindsay, a former Clinton administration official now at the University of Texas, said there was "nothing unusual or out of line" in Obama's stance.

"Was Richard Nixon weak because he went to China? Was Ronald Reagan weak because he met with (Mikhail) Gorbachev? History says no," he said.

As Obama moved closer to prevailing over Hillary Clinton in the state-by-state Democratic nomination fight, President George W. Bush stirred up the debate about talking to enemies.

In a speech to the Israeli parliament last week, Bush said that seeking to negotiate with "terrorists and radicals" was akin to the appeasement of Nazi Germany.

Obama, who took the comments as an attack on his views, accused the Republican president of using the "politics of fear." McCain weighed in, expressing astonishment that Obama, an Illinois senator, would want to meet with Ahmadinejad, who has called close U.S. ally Israel a "stinking corpse."

"My question is, what does he want to talk about?" McCain asked.

LIMITED TALKS ALREADY

But experts on both sides of the issue say the differences are less stark than the rhetoric suggests.

Michael Green, a former Bush aide who is now informally advising McCain, disagreed with portrayals of the Bush administration as being opposed to negotiations.

The administration has engaged in limited talks with Iran over its role in Iraq and with Syria on Iraq and other issues.

Green, an Asia expert now with the Center for Strategic and International Studies, was among the senior Bush aides who have negotiated with Pyongyang to try to get North Korean leader Kim Jong-il to dismantle the country's nuclear weapons program.

"You have to draw a distinction between diplomacy, which can be carried out at a variety of levels, and putting the presidency on the line for open-ended negotiations," he said.

Critics of Obama's stance include Clinton, who has said she would expand diplomacy with Iran and other adversaries but would be wary of offering a presidential-level meeting.

Such critics fear a top-level meeting could boost a leader like Ahmadinejad by giving him a stage.

Green said that was not an issue in the case of Reagan's meetings with Gorbachev or Nixon's talks with Mao because those leaders already had immense clout on the world stage.

But Lawrence Korb, who is advising Obama, has embraced the Illinois senator's stance, citing his own experience as a former Reagan administration official.

"There were hard-liners who didn't want Reagan to meet with Gorbachev," said Korb, of the Center for American Progress.

He faulted Bush for not engaging Iran after the Sept. 11 attacks on the United States after Tehran condemned the attacks and played a helpful role in Afghanistan. "Three months later, Bush put them on the Axis of Evil list," Korb said.

U.S. Defense Secretary Robert Gates on Tuesday questioned whether Washington could have productive talks with Ahmadinejad without first stepping up pressure on Tehran. He said there might have been a chance for useful talks in 2003 and 2004 while the less hard-line Mohammad Khatami was president.

"But what we have now is a resurgence of the original hard-line views of the Islamic revolutionaries," Gates said during a hearing on Capitol Hill.

A 2006 report by the Iraq Study Group -- a high-level bipartisan panel that sought to look for ways forward for the United States in Iraq -- recommended increased U.S. negotiations with both Iran and Syria.

Obama has calibrated his position on talking to adversaries since he outlined his view at a July 2007 Democratic debate.

Obama was asked then if would be willing to meet without precondition with the leaders of Iran, Syria, Venezuela, Cuba and North Korea during his first year in office, and said he would. He has since emphasized that though there would be no "preconditions" for his presidential meetings, they would take place only after a lot of staff-level preparation. (Editing by Frances Kerry and Mohammad Zargham) (To read more about the U.S. political campaign, visit Reuters "Tales from the Trail: 2008" online at http:/blogs.reuters.com/trail08/)

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