Robert Young, 91, a skillful and understated actor who began his career playing nice guys in films and went on to portray the sensible, kindly and patient title characters in two hit television series, "Father Knows Best" and "Marcus Welby, M.D.," died of respiratory failure July 21 at his home in Westlake Village, Calif. He had heart ailments.

Mr. Young appeared in more than 100 films, most of them in the 1930s and 1940s. His deft handling of both comic and dramatic roles was widely noted among critics and the public alike. But he was never a great romantic lead, and he never enjoyed the celebrity of such Hollywood contemporaries as Clark Gable and Errol Flynn. What made him a top star and a household name was television, with its smaller scale and greater intimacy.

"Father Knows Best" was a perfect vehicle for his talents. He played insurance agent Jim Anderson, a character as familiar and foolproof as mom's chicken soup. Anderson and his wife, Margaret, lived in Springfield with their three perfect children, Jim Jr., who was called Bud, and Betty and Kathy. In those days before women's liberation and political correctness, the girls were known to dad as "Princess" and "Kitten."

Mr. Young played the role on radio for five years before taking it to television, where it made its debut on Oct. 3, 1954. Besides the family, the program's featured characters included gardener Frank Smith, a naturalized citizen of Latin American origin who called himself "Fronk." The show stayed in production eight years and went into reruns for three more. Mr. Young won Emmys in 1957 and 1958.

"Marcus Welby, M.D." went on the air for the first time on Sept. 23, 1969. Southern California's kindliest physician, the aptly named Dr. Welby even made house calls. His young associate in the Family Practice Center at Lang Memorial Hospital in Santa Monica was Steven Kiley, a heartthrob (played by James Brolin) who got around on a motorcycle. Their receptionist and nurse was Consuela Lopez.

In 1970 and 1971, "Marcus Welby, M.D." became the first series on ABC to top the Nielsen ratings for an entire season. In 1970, it brought Mr. Young his third Emmy. The show ran until May 11, 1976.

Except for two reunions of the "Father Knows Best" cast and one for "Marcus Welby," Mr. Young made relatively few appearances in subsequent years. But in 1987, he starred in "Mercy or Murder?," a television drama based on a true story. Mr. Young played Roswell Gilbert, an elderly Floridian who shot his wife to death to release her from the sufferings of arthritis and Alzheimer's disease. When he was brought to trial, he took entire responsibility for what he had done.

"This is a strong, emotion-packed story," Mr. Young told an interviewer. "You don't get parts like this at 79 -- or at 29, for that matter."

He said he was particularly drawn to the story because he had struggled for years with alcoholism and depression. In 1966, he was hospitalized for exhaustion and alcoholism and withdrew from work until he began working on "Marcus Welby." He credited his wife, the former Elizabeth Louise Henderson, the high school sweetheart he married in 1933, with helping him through his illness.

In 1980, he was hospitalized for drug dependency.

In 1991, after a bout of heavy drinking, Mr. Young tried to take his own life at his home in Westlake Village by attaching a hose to the exhaust pipe of his automobile. He then called a tow truck for help in starting the vehicle. The operator noticed the hose and called authorities. The actor's wife said he had asked her to "form a pact with him" to commit suicide.

Robert George Young was born in Chicago on Feb. 22, 1907. His father, a building contractor, moved the family to Seattle and later to Los Angeles. While in high school, Robert appeared in plays, and his classmates voted him most likely to succeed in the theater.

For four years, he acted at the Pasadena Community Playhouse while supporting himself with jobs as a drugstore clerk, haberdashery salesman, bank clerk, loan company collector and reporter. In 1931, while touring with a play called "The Ship," he was seen by a talent scout for Metro-Goldwyn-Mayer. The result was a screen test and a five-year contract.

Mr. Young's first film was "The Black Camel," made in Honolulu. His other early work included "The Sin of Madeline Claudet," in which he appeared opposite Helen Hayes. His first comedy part was in "Vagabond Lady" in 1935. Photoplay magazine commented that he had "a kind of sparkle that he must continuously repress before the cameras when playing a serious role."

In 1936, Mr. Young went to London and made "It's Love Again" and "Secret Agent." Back in the United States, he had leading roles in "The Bride Wore Red," "Three Comrades," "Northwest Passage," "Western Union" and "The Trial of Mary Dugan."

In 1942, he appeared in three notable films: "Journey for Margaret," a story about an American reporter who befriends two English children during the London blitz in the early days of World War II; "Joe Smith, American," a story about a mechanic in a defense plant; and "H.M. Pulham Esq.," an adaptation of John P. Marquand's novel about an "inhibited, frustrated, baffled Boston gentleman."

Other Young films of the 1940s included "Claudia," an acclaimed romantic comedy in which his co-star was Dorothy McGuire; "The Enchanted Cottage," a story about a disfigured veteran that was based on a play by Sir Arthur Wing Pinero; and "Crossfire," which Mr. Young described as "a powerful indictment against antisemitism and other isms."

While his film career prospered, Mr. Young also made a name for himself in radio. Beginning in 1936, he made a number of guest appearances as a master of ceremonies for the NBC network. In 1941, he starred in Zane Grey's "Western Union" on the "Kate Smith Radio Hour." In 1944, he played the straight man to Frank Morgan on "The Maxwell House Coffee Time" program. "Father Knows Best" made its debut in August 1949. In addition to his wife, Mr. Young's survivors include the couple's four daughters, Betty Lou Gleason, Carol Proffitt, Barbara Beebe and Kathy Young; six grandchildren; and two great-grandchildren. CAPTION: Robert Young played insurance agent Jim Anderson on the 1950s television series "Father Knows Best." Here he is surrounded by cast members, clockwise from bottom left, Billy Gray, Elinor Donahue, Jane Wyatt and Lauren Chapin. Mr. Young also appeared in more than 100 movies.