A children's advocacy group wants the Department of Health and Human Services to oust Shrek, the animated ogre, from his role as spokesman for an anti-obesity drive.

The Campaign for a Commercial-Free Childhood says the soon-to-open "Shrek the Third" has too many promotional ties with unhealthy foods to justify using Shrek as a health advocate.

"There is an inherent conflict of interest between marketing junk food and promoting public health," Susan Linn, the group's director, wrote in a letter sent Wednesday to HHS Secretary Michael Leavitt.

"Surely Health and Human Services can find a better spokesperson for healthy living than a character who is a walking advertisement for McDonald's, sugary cereals, cookies and candy," said Linn, an instructor in psychiatry at Harvard Medical School.

HHS spokesman Bill Hall said the department had no intention of halting the public service ads, which were launched in February.

The ad campaign — which seeks to curtail childhood obesity — is a joint project of HHS, the Ad Council's Coalition for Healthy Children and DreamWorks Animation SKG, creator of the three Shrek movies. It features ads in which Shrek, a stout and often clumsy ogre, and his fellow characters urge children to exercise at least an hour a day.

"Shrek is a very well known character in the target population of this campaign," Hall said. "We have always promoted a balanced, healthy diet, which does not necessarily exclude the occasional treat."

Linn's organization — a nationwide coalition which monitors marketing aimed at children — said "Shrek the Third," which opens May 18, has promotional deals with dozens of food products, including Mars Inc.'s Snickers and M&M's candy; PepsiCo Inc.'s Sierra Mist drink; and Kellogg Co.'s Fruit Loops, Frosted Flakes, Pop-Tarts, Cheez-Its and Keebler cookies.

The film also has a tie-in with McDonald's; there will be Shrek-themed promotions of Happy Meals and DreamWorks will create animation for some McDonald's commercials.

"Why would young children follow Shrek's advice about healthy living and ignore his entreaties to eat Happy Meals and Pop-Tarts?" Linn wrote. "If government agencies are serious about combating childhood obesity, they should stop cozying up to industry and start taking real steps to end the barrage of junk food marketing aimed at children."

Penelope Royall, the HHS deputy assistant secretary for disease prevention and health promotion, stressed that the public services ads were using Shrek to promote exercise, not foods.

"Shrek is a good model, especially for children who can benefit from more exercise," Royall said. "He doesn't have a perfect physique, he's not a great athlete. ... We hope children will understand that being physically fit doesn't require being a great athlete."

A DreamWorks spokesman, Bob Feldman, defended the ad campaign and the Shrek promotions.

"We're proud of our partners, and together we're trying to be responsible marketers," he said.