WASHINGTON >>President Barack Obama has a new message: America has gotten its groove back.

In ways large and small, Obama has seized on a narrative of national optimism in recent weeks, offering a portrait of a country that, guided by him and powered by the American worker, is making a comeback. It is a narrative with strong echoes of President Ronald Reagan’s 1984 re-election campaign and one that is intended to provide a contrast with today’s less sunny Republican candidates.

And, of course, it is meant to suggest that Obama himself has hit his own stride.

“I placed my bet on the American worker,” he said Tuesday in a boisterously received speech at a United Auto Workers conference that was centered on his often-criticized bailout of the auto industry three years ago. “The American auto industry is back.”

In his State of the Union address in January, he went so far as to use the same three words that Reagan had in his own 1984 address: “America is back.”

For Obama, the theme is intended to turn the country into something of a running mate. While Mitt Romney, the Republican front-runner and often-unnamed foil in the president’s speeches, may say the country has lost some of its global power and economic might, Obama remains full of hope and confidence, in a strategy that harks back to his 2008 campaign.

Still, while Obama has enjoyed a strong few weeks with improving poll numbers and economic data, there is danger in the optimism strategy. Things could turn at any moment and make him seem out of touch, with oil prices rising and foreign policy crises looming in Iran and Afghanistan and with European debt.

Some liberals argue that the optimistic tone is out of step with the country’s mood and that a campaign highlighting his differences with Republicans on economic issues has more promise.

“America’s not back,” said Stanley Greenberg, chief executive of Greenberg Quinlan Rosner, a polling company that works with Democrats. “We have long-term fundamental problems with respect to personal debt, etc. If you look at our data and history, it takes a long time before job numbers translate into accepting at a personal level that things are better.”

Greenberg’s firm did a poll of 1,000 likely voters after the State of the Union speech, testing the “America is back” message compared with Obama’s other messages, and concluded that it is “by far the weakest,” according to a memo the firm put out after the poll.

Robert Dallek, the presidential historian, said: “I think optimism is always a good thing for a president to make the case for.” But, he added, “the issue is what will the economy be like in September and October?”

White House officials say that they are cautious about going too far into the optimism camp and that the president will try to explain the potential for a better future — provided, of course, that the country does not return to Republican policies that he argues helped lead to the crisis.

The Obama campaign is also trying to have it both ways, using the president to project a sunny picture while his top campaign aides continue to attack Romney on a daily basis — on television and radio, in emails and on Twitter.

Meanwhile, the president takes the high road. During his speech to the auto workers, he cited a string of statistics to make his point: “GM is back on top as the No. 1 automaker in the world, with the highest profits in its 100-year history. Chrysler is growing faster in America than any other car company.”

For Obama, it was the punctuation of weeks of high-profile outings in which he has spoken of U.S. exceptionalism.

On the same day Obama visited a Boeing plant in Everett, Wash., two weeks ago and showcased Boeing’s new 787 Dreamliner—“it’s lighter, it’s faster, it’s more fuel-efficient than any airplane in its class, and it looks cool,” he said — the campaign released a report about the resurgence of the U.S. manufacturers, arguing that Obama’s stimulus plan helped U.S. manufacturers to add nearly 400,000 jobs.

Three weeks ago when the Labor Department reported that the unemployment rate had fallen all the way back to the level of Obama’s first full month in office — 8.3 percent — Democratic allies held events outside of local businesses around the country touting the number and showing a jobs chart provided by the Obama campaign.

That chart, which shows U.S. job losses beginning to slow shortly after Obama took office, has been making the rounds on Facebook pages and Twitter feeds, courtesy of the always quick-to-share-and-post Obama campaign.

“The Republicans are running on a gloom and doom vision of American decline,” said Ben LaBolt, a spokesman for the Obama campaign. Obama believes that “if we promote policies that invest in the middle class, American will out-innovate and out-educate the rest of the world,” LaBolt said.

In his State of the Union address, Obama emphasized the country’s standing in the world, from its role in the Arab Spring to its tougher recent stance toward China. After pronouncing that the country was back, he declared, “Anyone who tells you otherwise, anyone who tells you that America is in decline or that our influence has waned, doesn’t know what they’re talking about.”

The new messageextends to Obama’s public mood. He seems to have cast off the gloom of last year and is instead trying to shape himself into a happy, likeable candidate. He chats up the reporters in the press cabin in the back of Air Force One and clearly enjoyed helping a student demonstrate a marshmallow shooter at a White House science fair.

The first lady, Michelle Obama, and first dog, Bo, recently stunned tourists visiting the East Wing of the White House with an appearance. And the president himself last week did another impromptu singing performance, taking the microphone at a White House jazz event to croon a verse of “Sweet Home, Chicago.” He had sung a snippet of an Al Green tune at the Apollo Theater in January.

“He’s channeling an appearance of positivity and optimism and patriotism, which are traditional positive virtues that most successful presidents trumpet when running for re-election,” said Edmund Morris, the author of Dutch: A Memoir of Ronald Reagan.

Ultimately, the success of Obama’s new theme, and his re-election prospects, may depend more on reality than on anything he says. Reagan enjoyed both a somewhat lower unemployment rate at this point in his first term — 8 percent — and higher approval ratings than Obama. An optimistic tone is far harder to project when the economy does not cooperate.

© 2012 The New York Times Company