A Network With a One-Track Mind

The fall season is only two weeks old, but ABC has already come up with a unifying theme for its series. On second thought, perhaps unifying theme is too highfalutin for what's really going on. See if you can detect what these ad lines for ABC shows have in common.

*THE COMMISH ''Tony goes undercover...to bust an X-rated movie racket.''
*LIFE GOES ON ''Jesse's nude painting of Becca makes her the talk of the town.''
*DOOGIE HOWSER, M.D. ''Doogie's caught with his pants down when he swims naked with his mom's sexy boss.''
*20/20 ''How to have better sex.''
*CIVIL WARS ''An art photographer convinces Sydney to pose nude.'' (And they mean nude; ABC even had to slap a viewer advisory warning onto the beginning of this episode.)

Add the fact that ABC's new Going to Extremes made its debut last month with a long shot of actress June Chadwick walking into the ocean in all her peekaboo splendor, and the trend is undeniable: ABC is becoming the Naked Network. But what's behind the back-to-nature movement? Several theories come to mind:

*The company has secretly changed its name, and its credo, to Anything But Clothes.
*The recession has finally hit ABC's parent company, Capital Cities, forcing severe cutbacks in the costume department.
*Now that the Murphy Brown contretemps is over, TV is eager to extend the run of that exciting ''family values'' debate.
*The shows represent a serious, earnest attempt to address issues of the flesh, which has absolutely nothing whatsoever to do with boosting ratings.

At press time, ABC's This Week with David Brinkley had no plans to incorporate nudity. Yet.