President Obama is exhorting supporters on the campaign trail to avoid rounds of boos or catcalls directed toward his Republican opponent, Mitt Romney.

The repeated efforts by Obama — used as recently as Tuesday at an Atlanta fundraiser — are intended to send a signal that he’s heading up a positive campaign even as he runs countless ads excoriating Romney’s business background.

It’s also part of a calculated effort to contrast his handling of the hecklers with Romney’s.

The presumptive GOP nominee has witnessed crowds at his events booing Obama but has not sought to quiet them.

And, in an interview on Fox News, Romney would not commit to urging his supporters and staff to stop the heckling.

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“I can assure you that we do not believe in unilateral disarmament,” he said, echoing earlier comments he made that “if you’re going to be heckling us, why, we’re not going to sit back and play [by] very different rules.”

Like Romney, Sen. John McCain John Sidney McCainAmerica's presence in Cam Ranh Bay should be more than occasional Meghan McCain, husband welcome first baby girl, Liberty Sage McCain Domenech The Hill's Morning Report - Sponsored by JobsOhio - Showdown: Trump-Biden debate likely to be nasty MORE (Ariz.), the 2008 GOP nominee, faced a slew of belligerent supporters.

Those attendees, however, took their Obama criticism beyond booing, including one woman at a Minnesota town hall who infamously called Obama “an Arab.”

McCain faced some initial criticism for not trying to quiet the crowds but, when he later sought to soothe his supporters’ emotions, instructing crowds to be “respectful,” he paid a price for their outbursts.

“John McCain certainly suffered when, after picking [Sarah] Palin, his audiences sometimes turned aggressive and even violent toward Democrats,” said Julian Zelizer, a professor of history and public affairs at Princeton University. “This pushed him toward the far right, rather than the center he always thought he could secure, and allowed Obama to fill the void.”

This election cycle, Obama has time and again praised McCain for being a much more reasonable opponent, seeking to portray Romney as extreme.

“John McCain believed in climate change,” Obama said at a fundraiser earlier this month. “John believed in campaign finance reform. He believed in immigration reform. I mean, there were some areas where you saw some overlap. In this election, the Republican Party has moved in a fundamentally different direction.”

Observers say Obama’s wagging-of-the-finger approach helps telegraph a message that the president is taking the higher ground by keeping the attacks away from the jugular. But it is also aimed at preventing unscripted YouTube moments and attacks from Republicans aimed at peeling away the crucial independent vote.

“The last thing Obama wants is to play into Republican charges that the president’s support comes from ‘dangerous’ and ‘lawless’ left-wing organizations, the kinds of attacks Richard Nixon used effectively in 1968 and 1972 to create an impression that the Democrats were not part of ‘mainstream America,’ ” said Zelizer.

Tobe Berkovitz, a professor at Boston University who specializes in political communication, added, “It positions your opponent’s supporters as not the kind of people independents can relate to.

“You want your supporters to be riled up, but you don’t want to make it seem like your supporters are haters and that you’re running a campaign bringing out the worst of the electorate,” Berkovitz said. “An unruly mob is a bad reflection on any campaign.”

Obama has tried to tamp down outbursts and unscripted moments on his side.

During a fundraiser in Atlanta, after the crowd booed at the very mention of Romney, Obama repeated a line he’s used in recent days to quell an overreaction from the crowd: “Mr. Romney is a patriotic American,” he said.

“He’s got a beautiful family,” Obama added. “He’s been very successful in his life.”

When the crowd laughed at that line, Obama once again sought to quiet the crowd, adding, “No, he has,” before quickly turning back to highlight their differences and contrasting approaches to handling the economy.

For more than a week — after a Romney campaign bus drove around an Ohio site where Obama was set to deliver a speech — the president’s campaign has tried to highlight its views on the matter, even sending out a press release urging Romney to focus on the issues.

“We have sent a strong message to our supporters that this campaign should be an open exchange of ideas, not one where we drown out the other side by heckling and crashing events,” Obama campaign spokesman Ben LaBolt said. “Campaigns are a reflection of their candidate, and Mitt Romney has a different view, endorsing heckling. With all that’s at stake in this election, Americans deserve better.”

But Obama “is graciously trying to have it both ways,” Berkovitz said, “by attacking his opponent and being magnanimous.”

At the same time, Republican strategist Ron Bonjean said it’s part of Obama’s strategy to “attack Romney from all angles.”

“His latest effort looks like he’s trying to play catch-up on being a nice campaigner even though everyone realizes that’s not the case,” Bonjean said.

Besides, Bonjean added, “Romney has already staked out the nice-guy niche for the campaign.”