Watching "20/20." the ABC newsmagazine which premiered on the network last night, was like being trapped for an hour at the supermarket checkout counter and having to read the front pages of blabby tabloids over and over again

"20/20" is the Top 40 radio of TV news an animated smudge on the great lens of television and probably the trashiest stab at candycane journalism yet made by a TV network.

For its first 20 minutes or so, the program was a kinetic explosion of shifting images in dizzying array - certainly impressive as a piece of tape editing but hard to distinguish in textures from the commercials. It was allzip-zip-zip, but it produced zilch. It looked like "Laugh-In," because it represents the same kind of bitz on the senses without really engaging the mind.

There is certainly not the briskness and authority of "60 Minutes" nor the wit and sophistication of Weekend" here. but as an laternative to those shows, "20/20" offers a sleazy choice we probably do not need.

The last half of the program was slightly more respectable than the first; it included a political portrait of and brief interview with California Gov. Jerry Brown who, in the breakneck spirit of opening night, was three times interrupted by interviewers as he answered their questions.

Earlier, a report by Sander Vanocur on the possibility of nuclear terrorism within the United States started on a tastelessly sensationalistic note (shots of the White House and the Capitol as we ere told how homemade nuclear bombs could de- (See 20/20, b13, Col. 4) (20/20, From B1) stroy them) but verged into fresh and informative territory with a look at the "NEST" team that ferrets out stolen nuclear materials with helicopters.

It was hardly enough to redeem the hour's honor, however.

Inexplicably chosen as cohosts for the program were the look alike team of Harold Hayes, a former Esquire editor, and Robert Hughes, an Australian-born art critic. What executive producer Bob Shanks saw in either of them is a mystery, unless he envisioned a news-team counterpart of "The Two Ronnies" of the BBC. Instead, the pair came off as Tweedle-Dum and Tweedle'Dum, with one of the Dum's having a distracting and irrating Aussie accent.

He produced Susan B. Anthony's last name as if she were Marc Anthony's sister.

"Hughes" and "Hayes," as they reffered to each other, sat on a desk in an overly elaborate media room and fake library, and occasionally correspondents materialized to report to them like students talking to their school counselor.

First to show up desk-side was the redoutable and self parodistic Geraldo Rivera, whose foray into investigative gernalism on the first show was an endless and dubiously important expose on how jackrabbits are killed during the training of grehounds. "The rabbits don't stand a chance," said Rivera, who spoke as usual in tones of sepulchral indignation and allied himself with all the enemies of evil who have ever exlisted, Batman and Robin included.

Rivera's on-the-job outfits are as flamboyant as his self-glorifying reportorial style. With a red bandana around his neck an an open Western-style shirt, he looked like someone who should be accompanying Ratso Rizzo down 42nd Street.

The news boys at the other networks must have been in stitches a sGeraldo hid in the bushes to watch the secret sale of jackrabbits. It was pretty funny, but the fact is that "20/20" looks like just the kind of show that would have hatched in the mind of the ratings mad programming executive in the movie "Network."

Even she might have had better sense, however, than to actually put it on the air.