Vienna's Volksoper, the most celebrated of operetta companies, will play at the Kennedy Center for two weeks next May as part of its first tour of the United States. The appearance also will mark the first time a European opera company has played the Kennedy Center since 1979.

The repertory will include Strauss' "Die Fledermaus" and Lehar's "The Merry Widow," those most popular of operettas, as well as Ka'lma'n's "Princess of Czardas."

The company of more than 200 will be in the United States for six weeks, beginning April 9 at Lincoln Center's New York State Theater. There will be single weeks in Chicago and Los Angeles, followed by the Kennedy Center run, starting May 7.

Traditionally, the Volksoper (People's Opera) has been Vienna's second resident opera company. After World War II, it shared its facilities until 1955 with the State Opera, whose home was severely bombed during the war. Since then it has concentrated on operetta and the Broadway musical, including widely praised productions of Cole Porter's "Kiss Me Kate" and Leonard Bernstein's "West Side Story."

The tour is to be sponsored by the Austrian government and Kazuko-Hillyer International Inc. management in New York.

The Austrian Embassy said yesterday funds have been raised for the Vienna Philharmonic to appear under Leonard Bernstein at the Kennedy Center during its winter tour, on Feb. 27 or Feb. 28. Previously, the Washington Performing Arts Society, which will sponsor the event, had planned to skip the Philharmonic because of the cost.