Here's Unca Walter in his ruddy-old-salt mood, sitting in an office sprinkled with nautical bric-a-brac. "Welcome back to our 'Universe,'" Unca Walter says, those singsong cadences already at full steam. Walter Cronkite is looking more and more like Mister Bluster, famous puppet codger of the old "Howdy Doody Show," but when he gets up from behind the desk, he brings to mind the senior citizen who does the veterans' life insurance commercials.

The funky-uncky approach doesn't work at all on "Walter Cronkite's Universe," the CBS News science magazine getting its second annual summer tryout starting tomorrow night at 8 on Channel 9 (after which it moves to Tuesdays). Cronkite's delivery sounds windily self-parodistic from the outset, and he's so eager to bounce viewers on his knee that he seems to have borrowed a page or two from Mister Rogers.

The half-hour is divided into three laggardly features, the first concerning underwater "bioluminescence," an eerie glow given off by some creatures of the deep. The Midshipman fish, for instance, lights up when sexually aroused, as who doesn't. The Sea Pansy brightens when bitten by a fish, by way of scaring the fishy away.

"Certainly scare me to bite into a Sea Pansy and have it light up," sez Unca Walter, har har har. He should have worn his yachting cap for this one, except he might look to much like the creaky Lothario played by Joe E. Brown in "Some Like It Hot."

He is the monarch of the sea, the ruler of the king's nay-vee. Oh, Unca Walter brings to mind a lot of different people while on the Good Ship Universe, but unfortunately they don't have much to do with the man who used to be known as America's most trusted newscaster.

Charles Osgood handles a feature on how science may help restore works of art that have faded in time. A computer is able to deduce how the Mona Lisa may have looked when first painted; it's a charming conceit, but the producers, they're terrified of having the reporters shut up and letting pictures speak for themselves. Even if the picture is the Mona Lisa.

CBS bought an old, but pretty, color movie about crystallization for the close, and Unca Walter gets to hold a $2 million diamond in his hand. A security guard stands by, and Cronkite says to him at the end of the show, with the diamond in his paw, "I s'pose you want this back now." If Unca Walter gets any cuter, they'll have to turn him into a sitcom. "Walter Cronkite's Universe" is only about three inches away from that as it is.