Last Tuesday at 4:00 pm, people who work in and around Detroit 's Civic Center were greeted with music and groups of colorfully-costumed dancers moving with al most dream-like grace in front of the Noguchi pylon at the foot of Woodward. With Detroit's riverfront as a backdrop, six Motor City dance troupes and two soloists gave an impressive display of the depth and breadth of the Detroit dance scène in the first presentation of Dancers' Showcase, a free outdoor concert initiated by the Detroit Metropolitan Dance Project and co-sponsored by the Detroit Council for the - 'il lln Detroit Recreation Dept., and the National Endowment for the Arts. Since dance s communication, audiences are vital to the dance community. Dancer's Showcase was able to bring Detroit's dancers to their audience (which isstill developing) and to an environment that had never before seen a dance performance. In that sunlight, every piece was something special, and the participants- Dance Detroit, the Metropolitan Ballet Company of Michigan, the soups dance troupe, the Writhm Dance Company, and soloists Barbara Levenson and Jean Raczkowski - amply demonstrated the competence and excellence of the highly-developed dancers who live and work here. As crowds gathered on Jefferson, even more people stopped to see what the crowd was all about. Several obviously delighted office workers stopped to ask a dancer, "Is this going to happen every day?"