Mary Caroline Pratt Herter, 84, the widow of former secretary of state Christian A. Herter, died Thursday in a hospital in Los Alamos, N.M.

A resident of Washington since 1941, she had been visiting a son in Santa Fe, N.M., where she suffered a stroke.

Her husband was a member of Congress from Massachusetts for 10 years, governor of Massachusetts, secretary of state in the second Eisenhower administration, and a trade negotiator in the Kennedy administration.

Like the wives of many public men, Mrs. Herter found her own role as a wife, mother and grandmother. She once said that some of her happiest years were 1953 to 1957, when her husband was governor of Massachusetts.

"A governor's wife is part of a governor's job," she once said. "During the two terms he was governor I was with him more than ever before."

Her other interests included painting and gardening, and the garden of the Herter home frequently was included in tours of Georgetown houses. She rode horseback into her 80s, and was fond of tennis, swimming and bridge.

After her husband's death in 1966, Mrs. Herter devoted much of her time to the Hearing and Speech Center at Children's Hospital. She also was active in behalf of the Arthritis Foundation.

Mrs. Herter was born in Brooklyn, N.Y. She was a granddaughter of Charles Pratt, an associate of John D. Rockefeller and founder of the Pratt Institute in New York. She was educated at Miss Porter's School in Farmington, Conn. The Herter's were married in Glen Cove, N.Y., in 1917.

In addition to their home in Washington, they maintained homes in Manchester and Millis, Mass. They also visited a family property in South Carolina and Mrs. Herter continued to go there until recent years.

Survivors include four children, Christian A. Jr., of Santa Fe, Mrs. Joseph P. Seronde Jr. of Stow, Mass., Dr. Frederick Herter of New York City, and E. Miles Herter of Manchester, Mass.; 15 grandchildren, and seven great-grandchildren.

The family suggests that expressions of sympathy be in form of contributions to the Hearing and Speech Center, Children's Hospital National Medical Center in Washington, or to the Christian A. Herter Center, 1175 Soldier's Field Rd., Allston, Mass.