Dr. Tomas Cajigas, 87, a pathologist and bacteriologist who taught and practiced in Washington for more than 50 years, died Wednesday at the Oak Meadow Nursing Home in Alexandria. He had a series of strokes and had lived at Oak Meadow for the last three years.

A native of Rincon, Puerto Rico, Dr. Cajigas came to Washington as an undergraduate at George Washington University. He earned his medical degree at GW in 1918 and for the next 13 years taught pathology and bacteriology at its medical school.

In 1922, he established his own laboratory. Over the years, he was a member of the staffs of several Washington hospitals, including Sibley Memorial, the old Casualty Hospital, now Capitol Hill Hospital, and the Columbia Hospital for Women. He became a specialist in gynecological pathology and taught that subject to interns and residents at the hospital.

In addition to his work with hospitals and other physicians, Dr. Cajigas had private patients, including the late FBI director J. Edgar Hoover. He was fluent in Spanish and French as well as English and for this reason he had a number of patients in the diplomatic community. He received several decorations from Latin American governments. He retired in 1970.

Dr. Dajigas contributed papers on his subjects to professional journals. Among his many professional affiliations were the following: diplomate of the American Board of Pathology, fellow of the American Society of Clinical Pathologists, fellow of the Medical Society of the District of Columbia, of which he was a founder, fellow of the American Society of Physicians, life member of the College of American Pathologists, member of the American Society of Bacteriologists, and member of the Academia Nacional de Medicina de Mexico. Dr. Cajigas received an honorary diploma from the Medical Association of Puerto Rico and was a founder of the Pan American Medical Society. He was a member of the National Press Club.

His wife, Anna B. Cajigas, died in 1974.

Survivors include a daughter, Anita C. Mattusch of Annandale; two sons, Dr. Tomas R., a physician in Bay City, Mich., and Paul A., of Mount Vernon, with whom Dr. Cajigas lived before moving to the Oak Meadow facility; three sisters in Puerto Rico; 14 granchildren, and three great-grandchildren.

The family suggests that expressions of sympathy be in the form of contributions to the Truro Episcopal Church, Fairfax, Va., for the needy.