NBC unveiled the second best news magazine program in network television last night, but since there are only three networks and three magazine programs, the feat is not precisely meteoric. Still, "Prime Time Sunday" with Tom Snyder got off to a slick, swift and efficient beginning, and after a summer's worth of shakedown, could well give some measure of competition to Mr. Number 1 on CBS, "60 Minutes."

The problem with the show is the way it tries to mix live studio segments from New York with film features from elsewhere. The show's first 18 minutes were probably its best, as a lively Synder was linked by satellite to British air travel entrepreneur Freddie Laker in London and to Langhorne Bond of the Federal Aviation Administration in Washington.

Safety problems of the DC-10 aircraft were the subject for this super-duper conference call, and if nothing new was added to the issue, at least Snyder, incomparably commanding in such situations, kept if moving briskly, even to the point of dismissing "Sir Freddie" - which sounds like something the president of NBC might be called - and sending him off to bed when he was no longer needed.

Then came the filmed segments - one on car repossessors and one on the author of sexy books for teenagers - and it was as if a live talk show were being interrupted for canned recorded material. The segments were all well produced, but they lacked the nearly Barrymorian theatricality of "60 Minutes." To get sizable audiences to tune in information in prime time, you must assure them your stuff has urgency, even if it takes the melodramatics and pizzazz of Cecil B. DeMille, which "60 Minutes" producer Don Hewitt certainly has.

"Prime Time Sunday" ended with a very funny feature on the non-mating of the two Chinese pandas at the National Zoo, produced by Clare Crawford-Mason who, like segment producer Craig Leake ("Repro Men"), is a holdover from the staff of "Weekend," the show Fred Silverman demolished to make way for Snyder's prime-time showcase. Last night's premiere did not justify the extermination, but neither did it rub salt in a nasty wound. It was not a cheap or gaudy production, as some may have feared.

Snyder does the show from an actual control room made photogenic for the air, so that viewers see the technical personnel and hear cross-talk between them. Perched before a wall of monitors, Snyder looks just a little like the champion salesman in a TV shop.

The technicians have to be kept within shouting distance, Snyder explained, because in future weeks "we will attempt so many things that could go wrong." The program's producer Paul Friedman could take pride in the fact that on the premiere nothing noticeable did. It is hard to recall the maiden voyage of any other program so technically complex that went off as smoothly.

Snyder was not as affably loose as on his late-night "Tomorrow" show, but even in the high-tech ambience, he did look mighty comfortable.

Then again, if one has the determination and self-confidence of a Tom Snyder, one would be able to look comfortable perched on the tippy tippy top of the Chrysler Building. Though his mammoth eyebrows seemed just a bit quivery at the show's start, Tom Snyder made it perfectly clear, crystal clear, and clear as acrylic floor wax last night that he has arrived with "Prime Time" in prime time intending to make it home. There is no point in trying to give such people "no" for an answer. That would be like telling Idi Amin to mind his manners. CAPTION: Picture, Tom Snyder