Dr. Frederick G. Evenden, 60, an ornithologist and executive director of the Wildlife Society in Washington from 1963 until he retired in 1978, and his wife, Mildred J. Evenden, 59, a former historical secretary with the Wildlife Society, drowned Feb. 20 in Benton County, Ore. They lived in Bethesda before moving to Eugene, Ore., in 1981.

The Benton County medical examiner's office said a mudslide pushed the Evendens' vehicle off a highway into Little Lobster Creek.

Dr. Evenden was a native of Woodburn, Ore. He earned his bachelor's, master's, and doctoral degrees at Oregon State University. He served with the old Army Air Forces in Southeast Asia during World War II.

Before the Evendens moved to Bethesda in 1963, they lived in California where Dr. Evenden was director of the California Junior Museum in Sacramento and a biologist with the U.S. Fish & Wildlife Service.

He was a former vice president of the Renewable Natural Resources Foundation in Washington and a former treasurer of the Washington Biologist's Field Club and the Rachael Carson Trust for the Living Environment. He was a board member of the American Institute of Biological Sciences and the National Conservation Committee of the Boy Scouts of America.

Mrs. Evenden was born in Salina, Kan., and raised in Corvallis, Ore. She was a 1949 graduate of Oregon State University. She was historical secretary with the Wildlife Society from 1964 until 1970.

The Evendens were members of Bradley Hills Presbyterian Church in Bethesda.

Dr. and Mrs. Evenden's survivors include two daughters, Angela G. Evenden of Corvallis and Jenne Ann, of LaGrande, Ore.; his sister, Millicent Olson of Lake Oswego, Ore., and Mrs. Evenden's sisters, Dorothy Crose of Idaho Falls, Idaho, and Ruth Jones of Corvallis.