Howard Lee Cook Sr., 75, a retired official of the old National Water Commission who was a longtime government specialist on water resources and hydraulic engineering, died of a heart attack Wednesday at Georgetown University Hospital. He lived in Bethesda.

Mr. Cook was deputy director of the National Water Commission from 1968, when it was established as a temporary agency to consider future U.S. water requirements, until its termination in 1973. He retired from the government at that time.

Mr. Cook worked as a hydraulic engineering in New York before coming to Washington in 1934 to head the hydraulics section of the Soil Conservation Commission. During World War II, he was a technical adviser on hydrology and flood control in the Agriculture Department's Office of Land Use Coordination and an official of the War Food Administration. After the war, he was a member of the natural resources staff of the secretary of Agriculture.

In the 1950s, Mr. Cook transferred to the Office of the Chief of Army Engineers and was deputy director of the Hoover Commission Task Force on Water Resources and Power. He later was chief of the special projects branch of the planning division and chief of the policy and legislative branch of the Army Corps of Engineerrs. He was awarded the agency's Meritorious Civilian Award in 1969.

A native of Cedar Rapids, Iowa, Mr. Cook earned a bachelor's degree in civil engineering from the University of Iowa in 1929 and was elected to Phi Beta Kappa.

Mr. Cook was the author of a number of articles and technical papers on water resource planning, hydraulics, hydrology and soil conservation.

He was a member of the American Society of Civil Engineers, the American Society of Mechanical Engineers, the Society of American Military Engineers, the American Geophysical Union and the American Meteorological Society.

His wife, the former Helen Louise Young, died in 1978.

Survivors include a daughter, Helen May of Bethesda; a son, Howard Lee Jr., of Silver Spring, a brother, two sisters, and three granddaughters.