In 1970, 4 percent of American kids were obese - three decades later, that number has more than quadrupled

Five-year-old Matt Felix grimaced Tuesday as he bit into a pod of sweet peas, declaring it "nasty." But the Rohnert Park kindergartner gave a thumbs-up to mangos, persimmons and apples.

Felix and his 8-year-old sister, Lorena, are among 62 children in a pilot program that public health workers launched Tuesday in a first strike against childhood obesity.

Hoping to combat this "silent epidemic," nurses, nutritionists and the Rohnert Park Boys & Girls Club have embarked on a twofold plan to teach good eating and exercise habits they hope will last a lifetime.

A precursor to chronic illnesses such as diabetes and heart disease, "obesity is going to be the number one public health issue in the United States in the next six years," said Lynne Conde, a registered nurse who's spearheading the effort through Sonoma County's health department.

In 1970, nearly 5 percent of U.S. children and adolescents ages 6 to 19 were overweight. By 2002, that number had risen to 16 percent, and health experts today put the number closer to 25 percent.

"We have a silent epidemic of childhood obesity," State Superintendent of Public Instruction Jack O'Connell said Tuesday. "We need to really refocus and redouble our efforts on physical fitness and appropriate nutrition for our children."

In Rohnert Park on Tuesday, the schoolchildren streamed into the Boys & Girls Club for games featuring candyless pi?tas, hula hoops and a taste test that challenged them to rate their produce preferences. Produce manager Juan Barreto from Roger Wilco Market passed around baskets of vegetables, quizzing kids about their vitamin content as children poked their fingers into the seedy, sticky middle of a freshly cut canteloupe.

Boys & Girls Club Executive Director Dan Hubley said he hopes what he and health workers started at his club in Rohnert Park will be adopted at other area Boys & Girls clubs. Conde sees the volunteer-driven program also spreading to classrooms throughout the North Coast.

Hubley likened the challenge to steering kids away from gangs.

"We're not trying to reverse obesity for the kid who's in kindergarten or first grade," Hubley said. "We want to get to these kids before they get obese."

While Conde prepared for weekly check-ins each Tuesday with the Boys & Girls Club members for the next three months, other Bay Area child advocacy leaders sounded the alarm about obesity.

The research and advocacy group Children Now, in a report card to be released today out of Oakland, gave California a "D" grade when it comes to childhood obesity. The group cited studies showing 28 percent of fifth-, seventh- and ninth-graders in the state are overweight, a jump of 6 percent since 2001.

Children Now spokeswoman Catherine Teare acknowledged the pressures on two-income families, where neither parent is home during the day to cook a nutritious meal. But she said parents and teachers as early as preschool need to instill eating habits that defy the fast-food, candy and soft-drink advertisements that inundate kids on TV and in print.

"Otherwise, nutritious foods are up against the juggernaut of food marketing," Teare said. "And who's going to win?"

Nutritionist Caryl Burns coordinates the nationwide Five-A-Day program in Sonoma, Mendocino, Lake, Napa counties and beyond, encouraging residents to eat five servings of fruits or vegetables daily. She and her colleagues concede it is tempting to grab a hot dog or pizza when you're whisking your child off to an after-school game. But they urge North Coast families to stock up on pre-cut vegetables, salads and whole-grain snacks that are now more available than ever.

"You create consumers," Burns said, before passing out trays of mangos and sweet peas Tuesday at the Boys & Girls Club.

"You have children for whom Cheetos or potato chips or a Snickers is the afternoon snack, and you let them taste jicama."