WASHINGTON DC, United States?First Lady Michelle Obama on Tuesday launched a major push against childhood obesity, which she has targeted as one of the greatest threats to America's health and economy.

The first lady joined President Barack Obama in the Oval Office as he signed an executive memorandum Tuesday putting in place an "obesity plan of action."

"I am so proud of the work that the first lady, along with the cabinet secretaries behind me, have done in trying to tackle one of the most urgent health issues that we have in this country," the president said as he signed the memorandum, surrounded by his senior aides and with the first lady's arm draped over his chair.

The presidential memorandum sets in motion a 90-day plan that "provides optimal coordination" among federal agencies to fight the obesity epidemic.

Michelle Obama, who has made child health and fitness one of the hallmarks of her tenure as first lady, was to be joined later Tuesday by members of her husband's cabinet, as well as luminaries from the media, entertainment, and sports worlds, to kick off the program at a White House event.

"We want to eliminate this problem of childhood obesity in a generation," Obama explained in a television interview broadcast Tuesday.

She said her efforts are aimed at providing more nutritious, affordable food in schools and giving children more opportunities for rigorous physical activity.

"One in three kids are overweight or obese and we're spending $150 billion a year treating obesity-related illnesses, so we know this is a problem and there's a lot at stake," she told ABC television's "Good Morning America" program.

Because of obesity and the illnesses associated with it, including diabetes, heart disease, and some cancers, the current generation of US children has been predicted to be the first to live shorter, less healthy lives than their parents.

The first lady, who before her husband's election was vice president of a Chicago hospital, was already on the warpath against obesity in the first year of President Barack Obama's administration.

She has highlighted healthy living by planting a vegetable garden on the lawn of the White and joining in physical activities?including showing off impressive hula-hooping skills?with US schoolchildren.

"We're launching a nationwide campaign called 'Let's Move,'" Michelle Obama told ABC television, adding that the importance of physical activity is something she stresses with her own young daughters, Sasha and Malia.

"My kids have to get up and move. They can't sit in front of the TV. I have my girls involved in sports because I want them as young women to understand what it feels like to compete and to win and to run and to sweat. This is about all of that as well," she said.

About 32 percent of US children and adolescents are obese or overweight, government statistics show. Almost 20 percent of children ages 6 to 11 and 18 percent of those ages 12 to 19 are obese.

Overweight children are at greater risk for weight-related health problems such as high cholesterol and diabetes, and have a higher chance of becoming obese adults.