Celebrating an anniversary makes sense if there has been a tradition. Arlington Dance Theatre -- marking its 30th birthday with performances last night and again tonight at the Thomas Jefferson Community Center on Old Glebe Road -- has little continuity to show save for its name. Artistic regimes have come and gone so haphazardly over the years that the anniversary program didn't even contain a list of past directors.

The names of Mary Craighill, Kathryn Fredgren and Carmen Mathe come to mind as having led three distinctly different versions of this troupe. Mathe (who happens to be visiting Washington right now with the Houston Ballet, for which she serves as a directorial assistant and principal mime) gave ADT its most professional and productive era. The current head of ADT is Kathy Robens Siegel.

Siegel's ensemble is largely amateur, and it tackles ballet, jazz dance and a variety of modern modes. Choreographers for the anniversary program were John Lechner, Marilyn Mazur, Rex Bickmore, Clovia Chinn, Adrian Bolton, Siegel herself and Liz Lerman. Only Lerman had the good sense to dispense with highly stylized movement. Her "Fanfare to City Dance" dates from 1980, when it was performed on the Mall, first by 300 Washington area dancers and then by the dancers plus their audience of more than 2,000 celebrants of the City Dance festival.

This time, on the Thomas Jefferson stage, there were 33 listed performers -- many of them coming from the auditorium to join the ADT regulars. They stood, legs spread apart, some facing the house and others turned away, as the music -- Aaron Copland's "Fanfare for the Common Man" -- began. Lerman's choice of movements was lean: Arms were lifted and lowered, bodies were bent at the waist, a few steps were taken, heads were thrown back, and eyes were raised. Using just a little patterning and nominal precision, Lerman succeeded in making her cast look like people at ease with themselves and with what they were doing.