* Campaign over, first lady loosens up
* Star power or saturation?
* Kids will remain her focus
CHICAGO, Feb 28 (Reuters) - First lady Michelle Obama knows she has star power, and she has used it for four years to champion her causes of fighting childhood obesity and helping military families.
But now that she has successfully made it through the last political campaign for her husband, President Barack Obama, the first lady is also having fun with her popularity - raising questions over whether she has gone too far in becoming a pop culture icon.
Her surprise appearance at the Academy Awards - where she was beamed in from the White House dressed in a sparkling evening gown to announce the Best Picture award - provided ammunition for her critics.
The first lady has enjoyed a steady positive approval rating over the past four years, even at times when her husband sank in the polls.
But the Oscar appearance - coming on the heels of the "mom dance" that she did with late night comedian Jimmy Fallon, which quickly went viral on the Internet - sparked a debate on the proper role of a first lady.
Washington Post columnist Courtland Milloy, who often writes about minority issues, described Obama's Oscar appearance as "unbecoming frivolity" and urged the first lady to "raise her game" and take up a more expanded role in the second term championing more serious causes.
"Enough with the broccoli and Brussels sprouts," Milloy wrote this week in the Washington Post. "Where is that intellectually gifted Princeton graduate, the Harvard-educated lawyer and mentor to the man who would become the first African American president of the United States?"
His column sparked hundreds of comments, ranging from people who thought Obama was doing a great job raising awareness about the childhood obesity problem to others who thought she was trying too hard to be like a Hollywood star.
The first lady said she was not surprised by the controversy over her Oscars appearance, but said she would use all forms of media to get out her message and would reach out to all demographics - including filmmakers who could help with her efforts to introduce children to arts and culture.
"Anyone in this position has a huge spotlight," Obama told a small group of reporters traveling with her on a three-city tour to promote her Let's Move program to fight childhood obesity.
"We've always thought about that spotlight. And taking it, while it's looking at you, to stand in front of something good so it shines on that too," Obama said, before jumping and dancing with more than 6,500 kids gathered in Chicago to highlight the importance of daily exercise.
NO JOB DESCRIPTION
Obama gained much of her popularity because Americans could relate to her, whether she was recounting stories of struggling to pay student loans early in her marriage with President Obama or talking about the difficulties of raising daughters Sasha and Malia on her own in Chicago while her husband worked as a U.S. senator in Washington.
As she travels about the country championing the Let's Move program, she talks of how she was forced into rethinking her daughters' eating habits several years ago after their pediatrician warned that they could be on the road to becoming overweight.
She said the Obama administration was the first to face such intense media scrutiny - from 24-hour news cycles to Twitter to innumerable blogs - so it was just inevitable that there was more of a focus on everything she does.
Her programs have shown some progress, with healthier school lunches now being served across the country and childhood obesity rates dropping in some states like Mississippi.
But should Obama be dancing on TV with a comedian dressed in drag or stunning 40 million viewers and the actors attending the Academy Awards?
"You don't really have a job description as first lady. And you're held up to this standard where it's impossible to please everyone all the time," said Anita McBride, former chief of staff to Laura Bush when she was first lady.
"I wouldn't say this has crossed the line. But coming on the heels of the very popular 'Mom Dance' ... It's saturating. You have to say - how much is too much?," said McBride.
Although the second Obama administration has only just begun, the first lady said she was aware that time was short for her to have an impact.
She said she planned to keep working on her two main projects - Let's Move and the Joining Forces military families program - but was also trying to decide what other causes she might champion in the next four years.
She said in the coming weeks she would decide what to pursue, but it would certainly focus on kids. Obama said she might begin to get more involved in the international arena but it would have to dovetail with her domestic projects.
Education Secretary Arne Duncan, in Chicago with Obama to announce a new public-private partnership to help kids get 60 minutes of exercise a day, said when the first lady was involved in a cause it added weight to the program.
"I think having the first lady leading that effort - as the mom-in-chief, as she's called - I think that can be really, really powerful," he said. "She is beloved, she is respected and I think people will pay attention."
A 2007 study said only 4 percent of elementary schools and 8 percent of middle schools provide daily physical education courses for the entire school year. (Editing by Claudia Parsons)