NBC is expected to announce its new fall schedule on May 2; ABC will follow on May 6; and first-place winner CBS will announce on May 10 . . .

Sunday night marked the end of the "official" 1984-85 prime-time race (the final ratings will be released today) and already two major ad agencies are predicting what viewers can expect next fall, when ABC, NBC and CBS have finished culling their new schedules from among 93 pilots . . .

According to Paul Isacsson, executive vice president and director of network programming and purchasing for Young & Rubicam, " 'The Cosby Show' has renewed network faith in comedy as a program genre. So it's no surprise that during the 1985-85 development season, comedy will return as the primary program form, after having been displaced by drama last year. Among comedy stars returning are Mary Tyler Moore, Flip Wilson, Valerie Harper, Loretta Swit and Suzanne Somers" . . .

But it won't be all comedies. About one-quarter of the new pilots are detective dramas whose heroes include housewives, robots, private eyes and even a rock singer who can shoot lightning bolts from his fingernails (in NBC's "Misfits of Science") . . .

The middle-class life style of much new TV is stressed by Philip Burrell, programming vice president for Dancer Fitzgerald Sample . . .

"Since realistic portrayals of contemporary life have proven popular ('The Cosby Show,' 'Hill Street Blues,' 'Miami Vice,' 'Kate & Allie,' etc.), many of the pilots, not surprisingly, are garnished with social relevance," Burrell said . . .

"However, the plot mix also includes such offerings as superheroes, science fiction, detectives, anthologies and madcap comedies, to provide a balance of alternatives from which the networks can make their final selections" . . .

NBC reportedly has already given an okay to "All Is Forgiven," starring Bess Armstrong as a soap opera producer and instant mother, and "The Golden Girls," dealing with three "mature women" living in Miami . . .

NBC has also lined up "Steven Spielberg's Amazing Stories"; "Blacke's Magic," starring Hal Linden as a retired magician turned crime-solver; and "Stingray," starring Nick Mancuso as a mysterious crimefighter who drives a '65 Corvette . . .

As we've reported previously, ABC is sold on "The Colbys of California," a "Dynasty" spinoff, and "55 Lime Street," with Robert Wagner as an international insurance investigator . . .

CBS has committed to "Twilight Zone," a one-hour weekly anthology with new writers -- including Stephen King, Ray Bradbury and Harlan Ellison -- who hope to recapture the old Rod Serling magic . . .

Middle-class black families will have strong representation on both the fall and midwinter schdules, as will other realistic themes, such as single motherhood, two-career marriages, midlife crises, teacher-student relations and out-of-work steelworkers starting new careers .