CBS Chairman William S. Paley has referred to Walter Cronkite as "Mr. America." Tonight Cronkite gets to be Mr. Universe, too, but there is some question about how long he will hold the title.

"Universe," the new CBS News science magazine show premiering at 8 on Channel 9, is a good idea whose time came when Geraldo Rivera was still in neckerchiefs. Geraldo Rivera still is in neckerchiefs? No matter. "Universe" is a solid, engrossing, perhaps too frantically illustrated but thoroughly commendable half-hour of television.

You'd think CBS News would be hot for the notion of turning it into a series, but no, network brass are decidedly cool.

Now this is a program about matter that matters. It opens with the 20-billion-year history of our universe compressed into one minute and fourteen seconds, and it continues with reports on the desperate quest to cure multiple sclerosis - focusing on the brillant cellist Jacqueline DuPre, who became it victim at the age of 28 - and on the virtual inevitability of a massive California earthquake. One expert says. "It might not occur for another 100 years, but it could happen tomorrow."

The stories are told with so many visual aids that anyone ought to find them lively at the very least. Indeed, executive producer and writer Ron Bonn may have overmulti'd on the multimedia bit. But one can understand the concern of a network newsman to make material as accessible as possible to as many millions of people as possible.

And yet Cronkite said yesterday from his office in New York that "it's true" that CBS News does not seem very keen on making "Universe" the series it deserves to be. Who cares about out old universe, anyway?

"The problem is a kind of strange psychotechnical one that is built into television," Cronkite said. "I noticed it when we made the pilot for the one-hour evening news a couple of years ago. You just cannot do pilots of news programs, and 'Universe' would be a news program because the whole geewhiz aspect of it is that each program would be tied to something that happened in the news that week.

"Now when you make a pilot in advance, you find that the bits and pieces get worked and reworked and put together and reworked again, until boredom sets in. You end up with no touch of the unexpected, and executive viewers become jaundiced about the whole project," said Cronkite.

The pilot for "Universe" could have been ready in January. It was in fact ready in March, but CBS wouldn't put it on the air during a crucial ratings period. They dumped it into June on the grounds that it can't do much harm.

Cronkite says the better way to do the show would be to give it a few airings and watch the reaction. "If we could just get on the air with it, it would develop over four of five presentations, go through a shakedown, and maybe turn into something pretty exciting," Cronkite said. "But the executive mind doesn't work that way."

Producer Bonn hadn't dreamed of approaching Cronkite to host the program when the idea was first presented to him a year ago. "He asked to see an outline of the first show," Bonn recalled yesterday, "and then later he handed me a note and said he'd love to do it himself." Asked if he would like Cronkite for the series, should it evolve, Bonn burbled: "Boy, would I!"

Asked if he could host the program and still anchor the CBS Evening News, Cronkite said: "I'd make any arrangement necessary to try to do it. I'd like to participate actively, in the sense of doing at least one story a week."

Cronkite has long has a passion for ecological, environmental and scientific stories and was patron saint of the space shots during the golden days of the Mercury, Gemini and Apollo missions. He is the perfect host for the program, partly because his mere presence helps demystify the subject matter and make it manageable for viewers. "Universe" becomes Uncle Walter's Old Curiosity Shop, and the proprietor clearly has tremendous concern with his inventory.

"What Walter essentially says to viewers," Bonn said, "is, 'Look, this isn't going to be so bad; you and I are going to go through this together.' One of our biggest problems is attracting women. I think women are scared to death of science, and, you know, it is comprehensible, it can be made understandable."

Cronkite helps immeasurably in making it so, or at least making it seem so.

"Universe" would help correct the shortage of science reporting on network television. Although we live in an exceedingly, sometimes maddeningly, technological age, science is covered meekly and with apparent reluctance by network news.

"It's such a wide-open field," Cronkite said, "and it's a totally unexplored and unexploited field. It is something television can do and ought to do exceedingly well."

Bonn hardly disagrees. "We're all geared up to go to series," he said. "I have two yards of file drawers filled with pieces I'd like to do. And the thing is, we would gear the show to the science aspects of the week's big stories. I've been dying this spring because of the show we could have done on Three Mile Island because if we were on the air we would have just torn out the show we had and done 'Universe' on Three Mile Island instead."

Bonn is aware of the discouraging rumblings coming from withing the CBS hierarchy - those brave souls who don't want any public affairs in prime time unless it's a barnburning moneymaker like "60 Minutes" - but he said: "I'm not hearing it officially and I don't want to hear it officially. It seems to me it would be damn foolish to drop the idea before it even gets a chance."

If "Universe" does become a series, Bonn said he would cut the 20-billion-year history down to 30 seconds. Imagine. But he wants to end it as he does on the pilot with a shot of a 20th-century, age-of-anxiety baby being born. "I'd want a new baby every week," Bonn said with the fervor of a visionary and a showman. "Black babies, brown babies, yellow babies, white babies - every different kind of damn baby there is!"

"Universe" is his baby now, and it remains to be seen whether CBS will let it grow up or pitch it into the Nile.

Walter Cronkite said he has his fingers crossed. CAPTION: Picture, Walter Cronkite on CBS' science show 'Universe' tonight.