Mary Hazell Harris, 81, a retired executive director of Defenders of Wildlife, died Wednesday at Sibley Memorial Hospital. She had cancer.

In 1963 she was named executive director of the organization, which claims 50,000 members in the United States. She also edited its publication, The Defenders of Wildlife News, now called Defenders Magazine.

Miss Harris held both jobs until her retirement in 1974. She was credited with helping secure an executive order in 1972 banning the use of some poisons that had been used on federal lands to kill predators.

The organization has been active in efforts to protect such animals as coyotes, bobcats and wolves as well as other wildlife. It also has sought to restrict such devices as leg-hold steel traps.

After her retirement, Miss Harris served on the board of directors and later was honorary president of the organization.

Miss Harris was born in New York City. She came to Washington, where she lived until her death, in 1929, and went to work at the Government Printing Office as a cataloguer. She was a librarian at the GPO and spent many years as a volunteer in behalf of wildlife causes. She retired from the government to run the Defenders of Wildlife.

There are no immediate survivors.