The doomsayers are already at it. And for good reason.
TV's new season is still about a month away (starting the week of Sept. 27, with a few exceptions), but already some industry experts are predicting mostly disaster for the debuting series.
Two of the most respected forecasts - the annual ''Network Television Report, '' put out by Dancer Fitzgerald Sample, an advertising agency, and ''Forecast,'' by industry analyst Herb Jacobs - are both predicting a season no better and probably worse than last year's, in which only about 1 out of 4 of the new series survived. Of the 24 new series being introduced this year, these experts are predicting just about the same percentage of success.
The ad agency gives a good chance for success to two new shows, both on CBS: ''Newhart'' (Mondays, 9:30 p.m.) and ''Gloria'' (Sundays, 8:30 p.m.). Two familiar faces star in these series, Bob Newhart in ''Newhart'' and Sally Struthers, of ''All in the Family,'' in ''Gloria.''
Mr. Jacobs agrees about ''Gloria, '' which seems on the way to becoming a shoo-in success, mainly because it is sandwiched between ''Archie Bunker's Place'' and ''The Jeffersons'' on Sunday night. But he also forecasts success for ''Bring 'Em Back Alive'' (CBS, Tuesdays, 8-9 p.m.) and ''The New Odd Couple'' (ABC, Fridays, 8:30-9 p.m.).
''Bring 'Em Back Alive'' is based on the real-life adventures of Frank Buck, and ''The New Odd Couple'' is the old ''Odd Couple'' but played by blacks.
Although Dancer Fitzgerald Sample gives a ''good chance'' rating only to ''Gloria'' and ''Newhart,'' the agency also gives runner-up spots to ''Matt Houston'' (ABC, Sundays, 8-9 p.m.), ''It Takes Two '' (ABC, Thursdays, 9:30-10 p.m.), ''Family Ties'' (NBC, Wednesdays, 9:30-10 p.m.), and ''The Golden Monkey'' (ABC, Wednesdays, 8-9 p.m.).
Both Dancer Fitzgerald Sample and Mr. Jacobs save their harshest words for ''Square Pegs'' (CBS, Monday, 8-8:30 p.m.), a comedy about two 14-year-old girls determined to be popular at all costs. According to the ad agency: ''Most of the casting is too old to be credible, and the story lines will play unbelievably to almost everyone except a random collection of young teen-age girls and their orthodontists.'' Mr. Jacobs told an Atlanta trade audience that the stars of ''Square Pegs'' are ''unattractive . . . unfunny . . . but at least they can't act.''
Two of the announced starters - ''Mama's Family'' (based on the ''Carol Burnett Show'' Eunice sketches but without Carol) and ''Mama Malone'' - have already been scratched from the NBC and CBS schedules.
''Mama's Family'' is being replaced by ''Taxi'' (just dropped by ABC) on NBC's Saturday night schedule (9-9:30 p.m.), and ''Mama Malone'' is being replaced by ''Filthy Rich,'' the summer season's surprise hit, on CBS (9:30 p.m. Wednesdays). Maybe this is just not Mama's year on TV. Other not-so-world-shattering changes: The title of ''Brass Monkey'' was changed to ''Golden Monkey,'' while the name of ABC's Thursday night entry, ''For Better or for Worse,'' has been changed to ''It Takes Two.''
Read what the experts say - but remember that historically the task of picking winners has defeated experts of all kinds. Ultimately, ratings are supposed to be a reflection of collective viewing habits. And based on the most recent prime-time viewing figures, more than 8 percent of viewers have either turned to cable or turned off TV altogether.
A study of the complete new three-network schedules - indicating merely more of the same lowest-common-denominator programming we have been getting each year - is a good indication of the reason for the continuing drop in viewership.