Marilyn L. Guerra, 68, an Upper Marlboro resident who was a retired landscape architect with the Prince George's County public works department and a volunteer at nature centers, died of cancer Dec. 20 at a daughter's home in Rockville.

Mrs. Guerra retired in the late 1980s after about 20 years as a landscape architect for the public works department. She oversaw the selection and planting of trees along county roads and the landscaping of grounds in new county housing developments and around county buildings.

She was a dance instructor at an Arthur Murray dance studio in Dupont Circle when she came to Washington in the early 1950s. By the late 1960s, she was working for Rockville City Parks as a landscape architect and helped design Twinbrook Park and Rockcrest Park, among others.

She was born in Rochester, N.Y., and graduated from Drake University in Des Moines in 1947. She served on the board of the Melwood Horticultural Training Center in Upper Marlboro and volunteered with developmentally disabled adults in Melwood's greenhouse, helping them raise plants. She also volunteered for the Clearwater Nature Center at Louise F. Cosca Regional Park in Clinton and gave bird-watching walks throughout Southern Maryland.

She was president of the North American Bluebird Society and a volunteer at the National Museum of Natural History.

Her marriage to Charles Guerra ended in divorce.

Survivors include five children, Helen Long of Elkins, W.Va., Charles Guerra of Jacksonville, Fla., James Guerra of La Verne, Calif., John Guerra of College Park and Catherine Manickam of Rockville; and 11 grandchildren.