ANY DOWNTOWN Washingtonian who can remember when Fairfax, Rockville and Hyattsville were faraway places with strange-sounding names can appreciate the phenomenal growth over the past 40 years of what is called the greater metropolitan region. The conversions of rural land and life into higher-and-higher-rise suburban societies have not come all that easily. Complex demands and the results of development have challenged local officials to grow with the times, to mediate between past and future. In Prince William County, where such adjustments are only now taking hold, James J. McCoart was one of the political figures who thought hard about these changes and listened well to his neighbors. Maj. McCoart, who died Monday at the age of 53, was a pivotal member of the county's board of supervisors from 1976 to 1982.

Jim McCoart, graduate of the old George Washington High School in Alexandria and the College of William and Mary, was a Marine who served in Vietnam during the war there and in Lebanon in 1958. After retirement in 1975, he taught high school social studies at Potomac High School in Dumphries, and helped coach freshman football and basketball teams.

As new people and industry began moving into Prince William, the board of supervisors became increasingly fractious. The old-style freewheeling country politicians weren't all taking kindly to development, and the newer/younger local leaders weren't all that tolerant of their seniors. Maj. McCoart ran and won as an independent from the Neabsco District and quickly established himself as a thoughtful public servant who could walk between the warring camps and deal in good humor with both of them.

Maj. McCoart recognized the importance of participation in the Washington Metropolitan Council of Governments, with its record of regional approaches to common problems, from water and air pollution to transportation and economic development. Prince William is grappling still with the prospects of more people and industries in tighter surroundings. But thanks to the contributions of Jim McCoart, there is understanding and vision in a county government seeking to serve a diverse and lively constituency.