Dr. Eleanor Lucille Long, 53, a pathologist at the Environmental Protection Agency, died of cancer Sunday at the University of Mississippi Medical Center in Jackson, Miss.

Dr. Long studied the effects of food additives and pesticides on the tissues of experimental animals to see if they caused adverse effects, including cancer. She had been engaged in this research at the EPA since 1971, and had done similar work at the Food and Drug Administration from 1958 until 1971.

Dr. Long was born in Washington and grew up in Memphis, Tenn. She received a medical degree from the University of Tennessee Medical School. She returned to Washington in 1953 as a senior resident at D.C. General Hospital. She was an assistant pathologist at D.C. General from 1954 to 1957, and then joined the federal government.

Dr. Long was a diplomate of the American Board of Pathologists and a member of the D.C. Society of Pathologists, the D.C. Medical Society, the Society of Pharmacological and Environmental Patholigists, and the American Medical Association. She had contributed to professional journals.

She was a member of All Souls Memorial Episcopal Church in Washington.

Survivors include her mother, Lucille Long, of Goodman, Miss.

The family suggests that expressions of sympathy be in the form of contributions to the American Cancer Society.