Mary O'Hara Alsop, 95, an author whose books include "My Friend Flicka," an enduring and enchanting story about a boy and a colt in the harsh and demanding wilds of Wyoming, died of arteriosclerosis Tuesday at her home in Chevy Chase.

"My Friend Flicka" appeared in 1941 and met with critical as well as popular success. It is the story of a 10-year-old boy, Ken McLaughlin, who lives on a ranch in Wyoming. His father, a former Army officer, raises blooded horses. But Ken decides that the horse for him is Flicka, a wild and beautiful filly who is all but untamable. Needless to say, Ken triumphs. a

But along the way he learns much about himself and the process of growing up. Not only is there love and conflict between the boy and the horse, but also the tension between the boy and his father, who does not approve of Flicka, and the sympathy of his mother, who does. And there is the setting: the windblown hills of Wyoming. The critic Marianne Hauser said the reader could "smell the grass and feel the coolness of the wind."

In 1944, Miss Alsop, who wrote under the name of Mary O'Hara, published a sequel, "Thunderhead," and in 1946 she published "Green Grass of Wyoming."

Of "Thunderhead," Orville, Prescott, a critic on The New York Times, wrote: "It is that rare achievement, a sequel to a great and richly deserved success that in no way disappoints or falls short of its distinguished predecessor. . . When other topical and fiercely contemporary books are long since forgotten, timeless tales like hers will always find a new public awaiting them as fast as new generations who like children and like horses grow up enough to read them. No writer that I can recall has ever written about animals of any kind the way Miss O'Hara does about horses, with such love and understanding, such blazing skill in individualizing them with striking personalities and yet with such absence of anthropomorphical romanticizing."

"Flicka" was made into a movie with Roddy McDowall playing the role of Ken. "Thunderhead" also became a film. "Flicka" went on to become a television series in the 1950s.

The book was translated into numerous foreign languages and still is in print. To the end of her life, Miss Alsop received fan mail about it.

Born Mary O'Hara Alsop at Cape May Point, N.J., she grew up in Brooklyn, N.Y., and was educated there. She spent two years in Europe studying languages. She also studied music. She began writing when she was a child and she once said that her work included her brother's school papers. A childhood ambition that had to wait many years for fulfillment was ownership of a horse.

In 1905, she married Kent Kane Parrot. They lived in California and there Miss Alsop had a successful career as a script writer during the silent film era. Her marriage to Parrot ended in divorce and in 1922 she married Helge Sture-Vasa. In the 1930s, she went to live in Wyoming, and this experience provided the background for her best-known books.

Her marriage to Sture-Vasa having ended in divorce in 1947, Miss Alsop returned to the East and made her home in Monroe, Conn. She had her maiden name restored as her legal name. She moved to Chevy Chase in 1968.

Her other books include "The Son of Adam Wyngate," a novel published in 1952; "Novel-in-the-Making," an autobiographical work published in 1954; "Wyoming Summer," which came out in 1963, and "The Catch Colt," a novella published last year in England. Miss Alsop also wrote a folk musical called "The Catch Colt" that was produced at Catholic University and at the Lincoln Theater in Cheyenne, Wyo., in 1964. At her death, she was working on "Prodigal Daughter," an autobiography.

Miss Alsop's survivors include a son by her first marriage, Kent Krane Parrot Jr., a retired Air Force colonel, of Chevy Chase, three grandchildren, and one great-grandchild.