People in many suburban neighborhoods find that the streets they live on practically invite them to stay in their cars. There is often simply no sidewalk, forcing some suburbanites to put on their running shoes and pedometers inside giant malls, clocking miles as they pass the various cookie stands, ice cream shops and bagel makers.

A vocal group of urban planners, especially those known as New Urbanists, have embraced the new studies as proof of their longstanding contention that small-town life is the best. Among other imperatives, the New Urbanists and their followers have cited beauty, nature and money as reasons to face down suburban sprawl, with its dependence on cars, and once again build old-fashioned neighborhoods with streets laid in tight grids. ''Now we can say there are physiological issues, too,'' said Peter Calthorpe, a New Urbanist architect and urban designer in Berkeley, Calif.

The studies issued last week are the clearest example yet that the planning and public health fields are beginning to speak each other's language on suburban sprawl. After focusing for years on Americans' diets, health experts have turned to assess the degree to which Americans' four-wheel lives contribute to obesity, hypertension, coronary disease, diabetes, asthma, even mental disorders like anxiety and depression.

''We do an environmental impact statement for a new subdivision, and we look at trees and birds and the rest,'' Dr. Jackson said. ''But we need to look at the impacts on human health.''

Stay-at-home wives have often complained about the isolation of suburbia, working parents point to the killer commutes and teenagers moan about the boredom. Now Dr. Jackson believes there are persuasive, if yet circumstantial, links between the suburbs and certain physical and mental diseases. If so, he said, the building of larger and larger suburbs might be viewed as a colossal mistake.

The study published last week in the American Journal of Health Promotion is the one most likely to alarm public health and planning specialists. The study's authors, Barbara A. McCann, research director of Smart Growth America, an anti-sprawl coalition in Washington, and Reid Ewing, research professor at the National Center for Smart Growth at the University of Maryland in College Park, developed a ''sprawl index'' to quantify the density of 448 counties nationwide and then compared government health data on 200,000 people living in those counties.

The results of the obesity study -- which accounted for variables like age, gender, race, diet and physical activity -- suggest that people in more sprawling suburban areas, like Geauga County, Ohio, and Walton County, Ga., weigh more (as much as six pounds more in the most sprawling areas) and have higher blood pressure than people in more densely developed areas like New York City.