Sister Maria, 80, an Episcopal nun who served as a chaplain at Washington National Cathedral and supported causes by participating in charity walks, died of cancer Sept. 6 at her home in Washington.

Sister Maria regularly volunteered at the National Cathedral, where she pastored and preached. As a volunteer chaplain, she was available to people who wanted to talk and participated in the noon services. She often walked around, checking on cathedral staff.

She also was a docent at the Smithsonian Institution's National Museum of Natural History from 1995 until this past summer. She taught school groups and other visitors about marine life and insects.

Nathan Erwing, manager of the Insect Zoo, said Sister Maria was good at engaging her audiences and interpreting the various exhibits. She would hold live insects for visitors to touch and was responsible at times for live tarantula feedings.

"When Sister Maria walked into the room, you knew it," he said. "She had a definite interest, love and stewardship for the natural world and for people." She always remembered people on special days with cards, notes and phone calls, he added.

Sister Maria was born Mary Leinau in Riverside, Calif. She graduated from the University of Redlands in California and, along with her new husband, began working to help children with special needs. She received a master's degree in psychology at San Francisco State University and worked as a psychologist and teacher in California.

In 1973, after her husband, Russell Wallin, died, she felt a religious calling and decided to go to Episcopal seminary. She graduated in 1976 from the Church Divinity School of the Pacific in Berkeley, Calif., and joined the Order of the Widows.

After seminary, she went to Israel to help bridge religious and cultural differences. While there, she lived in a Palestinian shelter in Eizariya, east of Jerusalem. She worked in the shelter with severely retarded children and troubled and abandoned women.

After about three years in the Middle East, Sister Maria returned to California, where she worked as health care aide in Fremont and began training for marathons.

In 1994, after developing breast cancer, Sister Maria moved to Washington to live with her younger sister and brother-in-law, Kathleen and James Owens.

She completed two Marine Corps marathons in her mid-seventies and participated in two Avon Walks for Breast Cancer. She also took part in charity runs for groups advocating racial and sexual equality, gay pride, the treatment of AIDS and other diseases.

Sometimes while training for her races, Sister Maria would "run around in shorts and with a cigarette dangling in her mouth," said her sister.

She was a member of St. Thomas Episcopal Parish in Dupont Circle.

Her son, Kenneth Wallin, also preceded her in death.

Besides her sister, of Washington, survivors include her daughter, Gretchen Wallin Sutton of Rodeo, Calif.