The Alvin Ailey American Dance Theater, which settled into the Kennedy Center Opera House last night for a two-week visit (the longest Ailey engagement here thus far), is celebrating its 20th anniversary this season. Survival being ipso facto a major achievement in the dance world, this is a milestone worthy of celebration.

And one of the aims of the company's programs this time around appears to be a demonstration of the breadth and durability of Ailey's contributions to the art. We'll be seeing 22 dance works by 10 different choreographers, including Ailey himself; the dances will range from the year of the company's founding (1958) to the present, capped by a world premiere on Feb. 15.

Last night's opener, combining revivals of three works by Talley Beatty with two reliable Ailey standbys, made for rather a monochromatic assortment, heavily weighted towards loud, fast, raucous music and relentlessly propulsive movement.

The company of two dozen dancers, moreover, wasn't performing at optimum level -- the ensemble was often frayed at the edges, and even the veteran soloists seemed to be just going through the motions much of the time, without the vivifying spark that has long been a company trademark.

Even so, the evening had its share of the qualities that account for the troupe's large, loyal popular following -- physical excitement at gut level, theatrical flair, and the comradely spirit of the dancers.

The traits that may have made Beatty's "Congo Tango Palace" and "Toccata" (both sections of his longer "Come and Get the Beauty of it Hot") seem fresh and invigorating in 1960 -- tense, slinky jazz dance embellished with African, Caribbean and classical motifs -- look pretty hackneyed today, in the absence of firm formal underpinnings.

If his "The Road of the Phoebe Snow," using essentially the same jazz vocabulary, retains its effectiveness, it's because the drama it outlines imposes a legible structure, as well as elements of stark contrast. At the center of this portrait of life on the wrong side of the tracks (the Phoebe Snow was a railway train) are two duets illustrating, in turn, the act of love as sexual hostility and as tender passion. The stylized gang mugging and rape which form the ensuing violent climax have not lost their harrowing impact with the passage of years. Sarita Allen and Ulysses Dove were especially convincing as the ill-fated lovers.

Dudley Williams was as affecting as ever in Ailey's modest solo, "Reflections in D," and even in a less than inspired performance, "Revelations" once again showed its staying power. Among the dancers, though, only Mari Kajiwara and Clive Thompson were able to pull out all the stops, in their "Fix Me Jesus" duet.