ABC's ``Roseanne'' edged NBC's ``The Cosby Show'' as prime-time ratings champ in the just-concluded 1989-1980 season, NBC announced Monday. ABC's Tuesday comedy starring Roseanne Barr averaged a 23.3 rating, two-tenths of a ratings point more than the Bill Cosby family comedy which has been first in the Nielson ratings for the last four seasons. ``The Cosby Show,'' wound up in second place for the season. Cosby's series has been on the air for six seasons, and Barr's series for two. Each ratings point represents 921,000 homes. Final figures for the 30-week season, which ended Sunday, won't be available until Tuesday. But network research analysts say that NBC will easily win its fifth consecutive season, with ABC coming in second, and once-dominant CBS in third place for the third straight season. Still awaiting final figures for the last three days of the season, Preston Beckman, NBC vice-president for research, said that NBC thus far had a 14.6 ratings average, ABC a 12.9 and CBS a 12.2 during the season. NBC's ratings are down by nine percent, ABC's are flat, and those of CBS are down by three percent, he said. He cited competition from cable, the fledgling Fox network, and independent stations as factors in the overall ratings drop. However, he attributed 25 percent of NBC's decline to the absence of three sports events it had in prime time during the previous season _ the Summer Olypmics, the World Series and pro football's Superbowl.