CHICAGO -- Health officials are warning that overeating and lack of exercise could soon cause more deaths than tobacco use, and they're launching a new campaign to convince Americans to shape up.

The government ad campaign embraces the concept that small steps -- like taking stairs instead of elevators and eating fruits and vegetables rather than high-calorie snacks -- can make a big difference in weight and health.

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"We're just too darn fat ladies and gentlemen ... and we're going to do something about it," U.S. Health Secretary Tommy Thompson said.

A new Web site -- www.smallstep.gov -- offers tips on tackling what federal officials Tuesday called a public health emergency.

Experts cite growing evidence that obesity kills.

A government study appearing in this week's Journal of the American Medical Association says poor diet and physical inactivity may soon top tobacco use as the nation's leading preventable cause of death.

But officials say they've come to realize that warning people to make drastic lifestyle changes may not work. Instead, they're going for the kinder, gentler approach.

"One thing I've learned in talking about healthy living is that guilt does not help people change the way they live," Thompson said.

Thompson also said that deaths related to poor diet and lack of exercise increased 33 percent in the last decade. The latest figures show 400,000 people died of these causes in 2000.