Even though classes have not yet started at UC Davis, seven intercollegiate athletic teams have already taken to the field, the streets, the courts and the pool for their 1994 fall seasons. The Aggie football, women's volleyball, men's and women's soccer, men's and women's cross-country, and men's water polo teams reported as early as Aug. 13 to begin preparations for their seasons. In all, 390 athletes are participating in UC Davis athletics this fall, says Doug Dull, assistant athletic director. Four teams -- football, women's volleyball, water polo and women's cross-country -- were listed among the top 20 Division II teams in the nation in preseason rankings.