Robert Young, an actor who created solid, wholesome, common-sense characters on television in ''Father Knows Best'' and ''Marcus Welby, M.D.,'' died on Tuesday night at his home in Westlake Village, a Los Angeles suburb. He was 91.

After a prolific career as a dependable film actor during Hollywood's golden age in the 1930's and 40's, he went on to even greater success in the two long-running television shows that were among the most popular of their respective decades. Mr. Young's television roles were built on integrity, clarity and kindness. Although ''Father Knows Best,'' which Mr. Young originated on NBC radio in 1949, was a classically wholesome and idealized portrait of family life in the Midwest, circa the 1950's and early 60's, Mr. Young insisted that the character he played, Jim Anderson, should be more realistic than other sitcom dads, who were often dimwitted.

''I'd like to be the father, but not a boob,'' he told a producer friend during the process of developing the radio show. He and the show's creators sought to portray ''what we thought would be representative of a middle-class American family, if there was such a thing,'' Mr. Young once recalled. ''There probably isn't, but that was what we were looking for.''

Mr. Young's portrayal of a strong and humorous father with no serious problems was all the more remarkable because he was privately battling personal demons, including alcoholism. He attended Alcoholics Anonymous meetings during the making of the show.

After its television debut in 1954, the half-hour show, in which Jim Anderson, his wife, Margaret, played by Jane Wyatt -- Mr. Young was the only member of the radio cast who made the transition to television -- had three children, was not particularly successful, and CBS canceled it in 1955. But so many viewers demanded that the show be reinstated, and urged that it move from 10 P.M. to an earlier time slot so that the whole family could watch, that NBC picked it up the following season and showed it at 8:30, initially on Wednesdays.

The show prospered on NBC and then back at CBS. In its 1959-60 season, its last with original episodes, ''Father Knows Best'' had its most successful year, ranking sixth among all television shows. Successful reruns followed on CBS and ABC until 1963.

Mr. Young ''never had any problems about being a prima donna,'' Billy Gray, who played the son, Bud, on the show said today. ''He was very generous as an actor.''

After ''Father Knows Best'' ceased production, Mr. Young said he had tired of the role and wanted to move on. Like ''Seinfeld,'' it was one of the rare cases in the history of television when production of a series ceased at the peak of its popularity. Mr. Young himself always defended the program but seemed fully aware of its white-bread style and shortcomings.

Adding subplots about illness or drugs or serious problems, he once said, ''would have been like taking a beautiful painting and obliterating it with black paint -- and that really would have turned the audience off.'' He added, ''We never intended the series to be more than a weekly half-hour of fun and entertainment.''

After a brief semi-retirement, which Mr. Young said he loathed -- ''When anyone says 'retire,' I say 'retire to what?' '' he once said -- he was cast in 1969 as Marcus Welby, a Santa Monica general practitioner who involved himself in the lives of his patient.

Grant Tinker, former chairman of NBC and then a television executive at Universal Studios (which produced ''Marcus Welby, M.D.''), recalled in an interview that Ralph Bellamy was set to play the role. ''Robert Young suddenly appeared and was sitting in my office,'' Mr. Tinker said. ''Someone had gotten him the pilot script. His opening words to me were, 'I want to be Marcus Welby.' '' Mr. Young got the part.

''There was a very sympathetic quality to Young as an actor,'' Mr. Tinker said. ''You can easily confuse him with a kindly doctor. He was also a guy who had a backbone. He was very determined.''

The one-hour show, with James Brolin as his youthful medical sidekick, had its premiere on Sept. 23, 1969, and was an instant success. It became the biggest hit in the history of the ABC network up to that time. Part of its initial success was a result of weak competition, with CBS and NBC opposing it with news documentary programs. But viewers clearly adored the show and remained faithful to it against stronger competition in later years. The show's last broadcast was in 1976.

Although the series itself, unlike ''Father Knows Best,'' dealt with serious problems like autism, blindness, LSD side effects, drug addiction and leukemia, Marcus Welby himself was something of a fantasy doctor who took a deeply personal approach to all of his patients. He treated not only physical ailments but the fears and family issues of each person.

''He's understanding and dedicated,'' Mr. Young once said of Marcus Welby. ''These are words that for some reason have fallen into disuse. I knew from the start that I had to come back and play this man.''

Mr. Young, who won two Emmys for ''Father Knows Best,'' won a third for ''Welby.'' He was also held in esteem by medical groups.

He was married to the same woman for more than 60 years. Mr. Young was 17, and in high school, when he met Elizabeth Louise Henderson, who was 14. They married in 1933. She died in 1994. Mr. Young is survived by their four daughters, Betty Lou Gleason, Carol Proffitt, Barbara Beebe and Kathy Young. He also had six grandchildren and two great-grandchildren.

Despite the characters he played and his public image, Mr. Young was a complex and, in many ways, troubled figure.

He had a history of alcoholism and depression. In 1991, at 83, he tried to commit suicide by running a hose from his car's exhaust pipe to the interior of the vehicle. The attempt failed because the battery was dead and the car wouldn't start. He later admitted that he had been drinking when he asked his wife to enter into a suicide pact with him and then tried to take his life.

Mr. Young, the son of an Irish immigrant building manufacturer, was born in Chicago on Feb. 22, 1907, the fourth of five children. The family moved to Seattle and then Los Angeles when he was a boy. As a teen-ager, Mr. Young wanted to be an actor. He took part in high school dramatics and, after graduation, studied and acted at night at the Pasadena Community Playhouse. He worked part time as, among other jobs, a drugstore clerk and loan collector.

His theater work and good looks stirred Hollywood's interest in 1931, and a screen test brought his first role in ''The Black Camel,'' a Charlie Chan mystery. Signed by MGM, Mr. Young soon appeared in an extraordinary number of films in the early 1930's: in the course of 4 years he appeared in 24 pictures, playing serious roles in many of them. He appeared in such films as ''The Sin of Madelon Claudet'' (with Helen Hayes), ''Hell Divers,'' ''Strange Interlude,'' ''Tugboat Annie,'' ''The House of Rothschild'' and ''Today We Live.''

Slowly, Mr. Young forged a career not so much as a top movie star, in the vein of Clark Gable or Gary Cooper, but as a dependable actor whom audiences enjoyed watching. His co-stars included Greta Garbo, Joan Crawford, Myrna Loy, Katharine Hepburn, Greer Garson, Norma Shearer and Jean Harlow.

Among his most noted pictures at MGM were ''Three Comrades'' and ''The Shining Hour'' (both made in 1938), ''Northwest Passage'' (1940) and two 1942 features, ''Joe Smith, American'' and ''Journey for Margaret,'' in which he played a war correspondent who befriends a British orphan. The film made Margaret O'Brien, who played the orphan, a star.

Perhaps his most memorable performance was in RKO's 1945 love story ''The Enchanted Cottage,'' in which Mr. young played a battle-scarred war veteran.

Some critics said Mr. Young's later films were some of his best, including ''Claudia'' (1943), ''Those Endearing Young Charms'' (1945), ''Crossfire'' (1947), ''Sitting Pretty'' (1948) and ''Goodbye, My Fancy'' (1951).

''I am a plodder,'' Mr. Young once said. ''My career never had any great peaks. But producers and directors knew I was reliable. So when they couldn't really get the big stars, they'd say, 'Let's get Bob.' As a result I always kept working, each time a little higher.''