PORTLAND – Six major corporations and the United Way of Greater Portland are banding together to try to curb childhood obesity, one of Maine’s most serious health concerns, in Cumberland County.

The corporations have agreed to donate $1.8 million over the next five years to the Greater Portland Healthy Weight Initiative, in which Portland and 10 other communities in the southern Maine county will be a testing ground. If successful, the program could serve as a model for the state.

Maine has New England’s worst obesity and chronic disease rates, and Maine pediatricians say they see more overweight children than ever.

A 2002 survey by the Centers for Disease Control and Prevention said Portland had one of the nation’s lowest adult obesity rates, 15 percent. However, Maine’s obesity rates overall hover around the national average, and about a third of the state’s kindergartners are overweight or at risk of becoming so.

Later this year, a marketing campaign that stresses healthy eating and physical activity is planned for schools, doctors’ offices, businesses and newspaper use. The initiative also could result in legislative proposals, sponsors say.

The effort plans to gauge success by comparing state surveys of children’s health between now and 2011, said Deborah Deatrick, vice president of community health at MaineHealth, Maine Medical Center’s parent company. Maine Med and MaineHealth are both donors.

“We are making a multiyear commitment of money and leadership to stop the increase in numbers of overweight, obese and physically inactive kids – and ultimately reverse that trend,” said Meg Baxter, president of the United Way of Greater Portland, which is leading the initiative.

Other donors include health insurer Anthem Blue Cross Blue Shield; Hannaford Bros. Supermarkets; and disability insurer UnumProvident and TD Banknorth.