Lee E. Koppelman, a planning visionary who during four decades fought to impose a regional agenda for economic development and environmental conservation across Long Island, died March 21 at Stony Brook University Hospital. He was 94.

As executive director of the Nassau-Suffolk Regional Planning Board from 1965 to 2006, Mr. Koppelman was instrumental in preserving tens of thousands of acres of farmland and open space in Suffolk County, protecting coastal wetlands and the underground water supply, creating Suffolk County’s park system, and preserving the vast Pine Barrens forest.

As an appointee beholden to elected county executives, Mr. Koppelman wielded little direct power. But as a nonpartisan expert planner, he won the respect of politicians, preservationists and developers. When Mr. Koppelman resigned as executive director in 2006, Mitchell H. Pally, vice president of the Long Island Association, a business and civic group, said, “There‘s been no one more significant to Long Island in the last 40 years.”