Leon G. Billings (courtesy of Leon G. Billings)

Leon G. Billings, a former aide to Sen. Edmund Muskie (D-Maine) and a key author of the Clean Air Act and other landmark environmental laws, died Nov. 15 at a hospital in Nashville. He was 78.

The cause was a stroke, said daughter Erin Billings. Mr. Billings, who was visiting family in Tennessee, had homes in Bethany Beach, Del., and The Plains, Va.

As staff director of the Senate environment subcommittee from 1966 to 1978, he was a primary author of the 1970 Clean Air Act, one of the first and most influential environmental laws in U.S. history and a foundation for current air pollution laws.

He also played a key role in the 1972 Clean Water Act, the primary federal law governing water pollution, and 1977 amendments to the air and water pollution laws.

He served as Muskie’s environment adviser for more than a decade and later was the Democrat’s chief of staff in the Senate and when Muskie was secretary of state under President Jimmy Carter.

Mr. Billings also directed the Washington politics program at the University of Southern California and served in the Maryland legislature, as a Montgomery County Democrat, from 1991 to 2003, focusing on environmental issues. He later ran a consulting firm and taught college courses on the Clean Air Act and other laws.

Leon Gregory Billings was born in Helena, Mont., on Nov. 19, 1937. His father edited and published a progressive newspaper, the People’s Voice, and his mother was a journalist. He graduated from the University of Montana in 1959 and spent several years in the Navy Reserve.

His first wife, Maryland Del. Patricia Harstad Billings, died in 1990 after 28 years of marriage. Leon Billings was appointed to her seat before winning election in his own right. (He was an unsuccessful candidate in 1986 for the Democratic nomination in Maryland’s 8th Congressional District, which included Montgomery.)

Survivors include his wife of 21 years, Cherry Allen Billings of Bethany Beach and The Plains; three children from his first marriage, Shannon Billings and Paul Billings, both of Silver Spring, Md., and Erin Billings of Washington; two brothers; and four grandchildren.

Tom Jorling, who was Republican staff director on the Senate subcommittee while Billings led the Democratic majority, said Mr. Billings “had tremendous skills legislatively and politically. He was respected and trusted by all members of the committee, majority and minority. His talent and skills led to the enactment of the foundational environmental laws of that era.”

Jorling said Mr. Billings was disappointed to see laws for clean air and water come under attack from President-elect Donald Trump and congressional Republicans but said the laws have survived previous attacks from the White House and Congress. Trump has called climate change a hoax and vows to cut back the role of the Environmental Protection Agency, which he describes as a job killer.

“Leon’s work helped prevent any wholesale efforts at eliminating or rolling back those statutes” in previous administrations, Jorling said. The current fight “would have been a new challenge for Leon.”