"UNFORTUNATE COMPUTER ERROR HAS RESULTED IN 118,000 bra cups in rectangular shape..."

The ad runs at the top of the personals column of the current Saturday Review, and all you have to do is look at the date, March 31, to know who placed it.

"... Probably good as cigar ashtrays or for storing playing cards... Rounder-than-Round Bra Co."

Norman Cousins, the publishing pixie, is at it again. It's getting so he doesn't even wait for April Fool's Day any more.

"Oh yes," said his secretary, "that's him. He's the guilty party, all right."

As editor of the magazine for nearly 40 years (he's now chairman of the editorial board), Cousins has his staff in a state of baroque jitters at this time of year.He is an apostle of laughter, for he believes that it saved his life in 1964, when he was so wasted by a crippling disease his doctors wrote him off.

To get his mind off the pain, he had nurses read E.B. White to him and later called for a projector and some old Allen Funt "Candid Camera" reels.

He laughed so loud they chased him out of the hospital.

Moving to a hotel, he started a regular therapy of Marx Brothers movies. Within months he was back at work full-time. He has written about it for the New England Journal of Medicine.

For the last year he has been lecturing at UCLA on psychobehavior, but don't think for a minute that the people at Saturday Review are breathing easy.

One year the publisher ordered a hot dog from the office vendor, spread mustard lovingly on it and bit into it. It was rubber. "Cousing," he muttered.

Another time the whole staff got notices of a vast office shakeup. Everyone had to move. Everyone got a number, and you found your number on the new layout. Some people were moved into the lobby, some were moved into the restroom, some simply disappeared. "Cousins," everyone muttered.

Last April 1 the staff found an ad for a "REUNION OF PIONEER STREAKERS"... and everyone relaxed. Whew, that wasn't so bad. The old man must be fading a bit.

Then they got notice from the printer that 300,000 copies had been printed upside down.

As it turned out, it was only their 50 copies that had been run upside down, but it was enough to age a few editors.

Cousins, 62, was in Washingon this weekend attending a meeting of the World Federationists. April Fool's may still be a whole week off. But at Saturday Review, people are already opening their mail with something like dread.