LOS ANGELES, Feb. 26 — Don Knotts, the skinny, lovable nerd who kept generations of television audiences laughing as the bumbling Deputy Barney Fife on "The Andy Griffith Show," died on Friday. He was 81.

Mr. Knotts died of pulmonary and respiratory complications at U.C.L.A. Medical Center in Beverly Hills, said Paul Ward, a spokesman for the cable network TV Land, which broadcasts "The Andy Griffith Show" and another hit co-starring Mr. Knotts, "Three's Company."

Mr. Knotts had a half-century acting career that included seven television series and more than 25 films, but it was the Griffith show that brought him television immortality and five Emmy Awards.

The show was on the air from 1960 to 1968 and was in the top 10 of the Nielsen ratings each season, including a No. 1 ranking its final year. It is one of only three series to bow out at the top; the others are "I Love Lucy" and "Seinfeld." The 249 "Griffith" episodes have appeared frequently in reruns and have spawned a large, active network of fan clubs.

As the bug-eyed deputy to Mr. Griffith, Mr. Knotts carried in his shirt pocket the one bullet he was allowed after shooting himself in the foot. The constant fumbling, a recurring sight gag, was typical of his self-deprecating humor.

Mr. Knotts, whose shy, soft-spoken manner was unlike his high-strung characters, once said he was most proud of the Fife character.

His favorite episodes, he said, were "The Pickle Story," in which Aunt Bee makes pickles no one can eat, and "Barney and the Choir," in which no one can stop him from singing.

"I can't sing," he lamented. "It makes me sad that I can't sing or dance well enough to be in a musical, but I'm just not talented in that way. It's one of my weaknesses."

Mr. Knotts appeared on six other television shows. In 1979, he replaced Norman Fell on "Three's Company," playing the would-be swinger landlord to John Ritter, Suzanne Somers and Joyce DeWitt.

Early in his television career, he was one of the original cast members of "The Steve Allen Show," the comedy-variety show from the late 1950's. He was one of a group of memorable comics backing Mr. Allen.

Mr. Knotts's G-rated films were family fun, though not box-office blockbusters.

In the part-animated 1964 film "The Incredible Mr. Limpet," he played a meek clerk who turns into a fish after he is rejected by the Navy.

He was among an army of comedians, including Buster Keaton and Jonathan Winters, in the 1963 comedy "It's A Mad, Mad, Mad, Mad World." Other films include "The Ghost and Mr. Chicken" (1966); "The Shakiest Gun in the West" (1968); and a few Disney films like "Gus," (1976) and "Herbie Goes to Monte Carlo" (1977).

In 1998, he had a pivotal role in the back-to-the-past movie "Pleasantville," playing a folksy television repairman whose supercharged remote control sends a teenage boy and his sister into a sitcom past.

Born in West Virginia, Mr. Knotts began his show business career before he graduated from high school, performing as a ventriloquist locally. He was a speech major at West Virginia University.

"I went to New York cold," he recalled in a visit to his hometown, Morgantown, where city officials renamed a street for him in 1998. "On a $100 bill. Bummed a ride."

Mr. Knotts soon landed a job on a radio western called "Bobby Benson and the B-Bar-B Riders," playing a wisecracking, know-it-all handyman. He stayed with it for five years. Then came his series debut on "The Steve Allen Show."

He married Kay Metz in 1948. The couple had two children before divorcing in 1969. He later married, then divorced Laralee Czuchna.

In recent years, he said he had no plans to retire, traveling with theater productions and appearing in print and television advertisements for Kodiak pressure-treated wood. He treasured his comedic roles and could point to only one role that wasn't funny, a brief stint on the daytime drama "Search for Tomorrow."

"That's the only serious thing I've done," he said. "I don't miss that."