The Ballet Theater returned to Boston last Monday night after an absence of two years to let the public see a week of good dancing again. Unlike two years ago, when this same company played to a near-empty theater, the Opera House on opening night was filled to capacity.

There were two Boston premieres in the Ballet Theater's program for Monday. The first of these was Agnes De Mille's "Fall River Legend," which is "suggested by" the story of Lizzie Borden, who "took an axe and gave her mother 40 whacks." It is an interesting theater-piece, but made so mostly by the miming of Nora Kaye and the sets of Oliver Smith.

Miss De Mille is perhaps more generally known for her choreography in "Oklahoma!" and "Carousel," and the parts of "Fall River Legend" which seemed the best were those dealing with the townspeople, who can be alternately gossipy, jubilant, and mournful. Miss De Mille is a spontaneous humorist and her townspeople are quite familiar. It is, oddly enough, in the dances of Nora Kaye that the interest lags and apparently Miss De Mille has nothing much to say, except that the murderess was a lonely, rejected girl. It is a tribute to Nora Kaye's dramatic abilities rather than her recognized dancing talents, that "Fall River Legend" is saved from the lugubrious. Her dancing with the image of her mother (Diana Adams) is an effective bit, however. The ballet suffers from being too long for its content, and from the Morton Gould music.

The other new ballet was George Balanchine's "Theme and Variations" which uses music of Tchaikowsky. It is one of those abstract jobs, with no book but with lots of opportunity for the corps de ballet and the soloists to show their stuff. The soloists were Igor Youskevitch and Maria Tallchief. Mr. Youskevitch is generally regarded as the best classical male dancer in the country, but he seemed Monday night, with all his technique, to be lacking in vitality and fire. But the highlight of the evening was the performance of Miss Tallchief. She is an exciting new classical dancer of unique beauty.