In St. Paul, Minnesota, music-lovers know that small is beautiful. The city has the smallest professional orchestra in the U.S. and one of the best.

The St. Paul Chamber Orchestra has come into its own this year, partly because the world has begun to notice the spectacular conducting talent of music director Pinchas Zukerman (who has long been known as a solo virtuoso on the violin and viola) and partly because two of its favorite composers have important anniversaries: Haydn's 250th and Stravinsky's 100th.

The 32-member group, the only full-time professional chamber orchestra in the country, emphasizes music of the 18th and 20th centuries, avoiding standard Romantic repertoire that usually calls for a much larger orchestra. The orchestra's series at the Kennedy Center, beginning on June 3 and continuing June 11 and 12, will focus on Haydn and Stravinsky but will also include three of Bach's Brandenburg Concertos and Beethoven's Second Symphony.

This kind of programming, aided by Zukerman's charisma, has made the orchestra a smashing success in the St. Paul-Minneapolis area. Season subscriptions have increased 65 percent in the past year, and the orchestra's earned income has increased 190 percent since Zukerman became the music director. Now in his second season, Zukerman already has contracted for 1985-86.

Beyond about 70 home concerts a year, the orchestra performs some 50 on the road. The orchestra has already played twice at the Kennedy Center during the past year and is beginning to find a steady audience in Washington -- partly, perhaps, because its concerts are being broadcast regularly on WETA-FM (10 a.m. Mondays).