"Swan Lake" and "Romeo and Juliet" will return to the Capitol Theater, and two world premieres are on the docket for Ballet West's 1989-90 season, recently announced by artistic director John Hart. The company will also go to an eight-performance season, rather than their present six-performance format, opening on Friday nights rather than Wednesdays.

Ballet West will open with "Swan Lake" in a special 10-performance run, Sept. 15-23. With choreography by Marius Petipa and Lev Ivanov, this romantic ballet is set to one of Tchaikovsky's most popular scores. Sets and costumes are by Peter Cazalet.John Hart, who will stage the work, learned the choreography at Sadler's Wells Ballet, where it was taught by Nicolai Sergeyev, who brought the masterpiece to the West. Hart will make a few cuts, rearrange numbers and add some new choreography, notably in the first act, to consolidate and tighten the production somewhat.

A triple bill Nov. 10-18 will feature two world premieres. Peter Anastos promises black comedy in "The Gilded Bat," the story of a little girl who realizes her dream to become a ballerina. It`s based on a comic strip by Edward Gorey, illustrator of PBS's Mystery Theatre, who will design the sets and costumes.

Val Canaparoli returns with his third company work, "White Mourning," with music from Schubert's "Death and the Maiden." Also programmed is Balanchine's "Allegro Brillante," set to Tchaikovsky's Third Piano Concerto in E flat.

Feb. 16-24 will see the return of Michael Smuin's "Romeo and Juliet," with score by Prokofiev, which the company premiered so successfully last September and has danced to popular acclaim on tour. "Of all the balletic versions of `Romeo and Juliet,' this is the one must suited to our company," said Hart.

The season will conclude March 30-April 7 with "An Evening of Shakespeare," celebrating the enormous influence of the Bard's works on the world of music and dance. Highlighting a program still to be finally selected will be Sir Frederick Ashton's "The Dream," with music by Mendelssohn.

The company will also dance its popular "Nutcracker" in Willam Christensen's choreography, Dec. 14-30 in 20 performances.

Season tickets are already on sale at the Ballet West box office in the Capitol Theater, 533-5555. "Nutcracker" tickets are sold separately from the regular season, but may be ordered at the same time.