Two dance groups appeared yesterday at Glen Echo Park: Tandem, which described itself as "post-modern," looked professional; the Prince George's Ballet did not. Was the reason for the crucial difference due to the technical proficiency of the performers, the quality of the choreography, the inherently greater difficulty of academic ballet or a double standard we use in judging classical and experimental work?

Elesa Rosasco and Kate Jacobs, who arranged and danced the Tandem program, happen to be ballet-trained. They are not virtuosos, and probably would be no surer in the academic vocabulary than the Prince George's dancers. But as choreographers, Rosasco and Jacobs worked skillfully within their own limitations as performers. Using undisguised classroom material austerely, with only slight variations, there were few passages of sustained development and no suprising transformations. Often, the two danced the same movements simultaneously or in sequence, while touching each other. However, these post-modern formulas were not followed slavishly. What was added were suggestive layers of sensuality or referential meaning that subtly distinguished the different Tandem pieces.

Strict ballet is more difficult to perform easily than most modern dance forms and we probably do have a slight double standard, but the Prince George's choreographers -- Gloria Isaksen, Leslie Smith and A.V. James -- might have shown more imagination in working around their performers' shortcomings.