PALM SPRINGS, Calif., April 26— Don Wilson, the rotund announcer who was Jack Benny's foil on radio and television for more than 40 years, died Sunday of a stroke. He was 81 years old.

Mr. Wilson was found unconscious at his home in Cathedral City and was taken to Eisenhower Medical Center. Doctors were unable to revive him and gave the cause of death as a cerebral vascular accident.

Mr. Wilson had lived in the Palm Springs area for about 10 years, where at one time he was host of a radio and television show. He and his wife, Lois Virginia Corbet, occasionally appeared in the theater. He was last in ''The Big Broadcast of 1944,'' which toured in the East with Dennis Day, who had been the singer on the Benny show; Gordon MacRae, and Harry James and his orchestra.

Mr. Wilson joined the Jack Benny radio show in 1933 after working as a sports announcer for NBC. He was the announcer, but he soon became a character on the show. His wife also eventually became a character on the radio and television shows, along with Eddie (Rochester) Anderson, Dennis Day, Phil Harris, Mary Livingston, Artie (Mr. Kitzel) Auerbach, Mel Blanc, Bea Benaderet, Verna Felton, Frank Nelson and others. Sneaking in the Commercials

''He was a great foil for Jack,'' said Irving Fein, the producer and longtime associate of Mr. Benny. ''He was the hearty announcer who tried to get the commercial on the air and Jack would try to thwart him. Sometimes Don would have the Sportsmen Quartet sneak in the commercial. Don would tell Jack the Sportsmen were going to do a song. Then they would sing a chorus of a song. Don would then tell Jack they had one more chorus - and they would sing the commercial.''

Mr. Wilson also spent a year as the announcer on ''The Kraft Music Hall'' and on ''The Tommy Riggs and Betty Lou Show,'' both on radio. The Jack Benny show began on radio in 1932; the television version began in 1950. It ended in 1965. Mr. Wilson was married to Miss Corbet, a radio actress, in Santa Barbara in 1950. It was his fourth marriage and her first.

Donald Wilson