Merv Conn, 91 , an accordionist whose oom-pah-pah polkas and renditions of Beatles pop tunes enlivened Oktoberfest fetes, Washington Senators baseball games and audiences at the White House, died Dec. 20 at the National Lutheran Home in Rockville.

He had complications from prostate cancer, said his son, Robert Conn.

There was no event too large or too small for Mr. Conn, perhaps the Washington area’s premier strolling and singing accordion player. He had a repertoire of more than 1,000 songs — a tune for nearly every occasion.

He performed at bar mitzvahs and weddings, Christmas parties — even though he was Jewish — official embassy soirees, concerts on cruise ships, ice cream socials and private recitals for presidents Truman, Johnson and Nixon.

From 1964 to 1969 he was the “Senators’ official music man” and played an electric accordion over the public address system between innings at home games in Washington.

Beginning in the mid 1940s, Mr. Conn gave accordion lessons from his studio on 14th Street NW, near Columbia Heights.

At one time, he employed five instructors who taught more than 300 students a week. Mr. Conn personally taught President Richard M. Nixon’s daughters how to play the accordion.

Mr. Conn said the popularity of the accordion diminished, however, with the rise of four lads with shaggy hair from Liverpool.

“The Beatles killed the accordion,” Mr. Conn told The Washington Post in 1996. “The sound of the accordion wasn’t the sound the young people wanted. . . . They wanted the sound of the guitar. After that, everything went downhill.”

Mervin Aaron Cohen was born Feb. 19, 1920, in Washington. He took the Conn surname later as a musician.

He was a 1937 graduate of Central High School and a 1940 accounting graduate of the old Benjamin Franklin University, now part of George Washington University.

During World War II, he worked as an auditor for the Treasury Department. It was there he met Rhoda Silverman, whom he married in 1942. She died 1989.

Survivors include two children, Robert Conn of Silver Spring and Maria Cohen of New York.

Mr. Conn began playing the accordion as a teenager. He got his start as a professional musician playing local events and on radio programs.

Mr. Conn wrote his own compositions and hundreds of arrangements of popular tunes. He had his own renditions of “The Entertainer” by Scott Joplin, Edith Piaf’s “La Vie en Rose” and John Philip Sousa’s “Washington Post March,” which he once performed for Washington Post editors.

“I can express myself with the accordion,” he told The Post in 1996. “It’s like an extension of my body.”

Mr. Conn said that since the 1950s the accordion had earned a bad rap from a listening public whose only exposure to the instrument was “Lady of Spain.”

“There’s nothing wrong with the accordion,” Mr. Conn told The Post in 1984. “It’s wrong with the accordion players.”