Suppose they gave a party and everybody came but nobody knew why.

It's happening in Detroit right now, and the television networks are all but blowing their tops in the attempt to make something terribly meaningful out of the Republican National Convention. First night's coverage actually was pretty entertaining -- until the "entertainment" started, that is.

Wayne Newton, looking like a used car salesman you wouldn't even want your daughter to speak to, was scarecly into his Las Vegas lounge-lizard version of the "Battle Hymn of the Republic" when NBC's able-brained John Chancellor observed, "The New York delegation watched the beginning of the show got up, and went home."

It was clear Chancellor and other network correspondents wanted to do the same. And as for the American people, they didn't have to get up and go home because they already were home and early ratings show they were avoiding the Republican National Convention like they'd avoid a cookout on Mount St. Helens. New York overnights showed that some 73 percent of those with their sets on chose to watch something other than the "Here's Ronnie" show playing on the three networks.

Apparently there's not much appetite out there in Television Land for bathiosis grandiosis -- trumped-up sentimentality on an "Apocalypse Now" scale. There was something vaguely impressive about Gerald Ford finding his second wind (or was it his first) with his "Bah-loney" speech, it's true, especially since its subtext amounted to, "You're more miserable now than you were under me." And there was something weirdly self-parodistic, too, about the fact that he almost dropped the "solid gold" medal the Republican poo-bahs presented him.

Chevy Chase has been replaced. The spoofed has become the spoof.

But the network news departments proved themselves agile to the point of double-jointedness in breathing a little life into what seemed plainly the Olympics of futility, not just an exercise in it. NBC's coverage was great, CBS's was good, and ABC's was sloppy and slipshod, just as one might have expected.

NBC News gave the event the benefit of every doubt, staying with official proceedings more often than the other networks, communicating most effectively the sense of the occasion, and devoting seven hours and 17 minutes to the convention on its first day, as opposed to just over six hours from CBS and less than five hours from ABC. (These totals don't include regularly scheduled newscasts but do include special editions of the magazine shows "60 Minutes" and "20/20.")

So much was said in advance about the GOP convention being a sleepwalk tht this may have become a self-fulfilling prophecy. But the fact is, watching lots of people bumble around in funny hats and with some of their inhibitions relaxed is still good television, and it's good Americana, too. And NBC had the good sense to put lots of people and lots of funny hats on the screen, to visually remind viewers that there in that hall are, indeed, representatives from nearly every corner of a country that still prides itself on diversity and variety. It was like a real "Real People."

Meanwhile, on the CBS "60 Minutes" broadcast, the tone of self-satire was clearly established by the indeflatable Mike Wallace, who poked at Gov. Reagan with intimidating questions like, on the subject of a running mate, "You mean to say you haven't got your mind made up?" and, on the subject of import quotas, "You mean you don't know this yet? It's pretty important!" o

See here, Reagan, what is this -- you trying to put something over on MIKE WALLACE?

For another guardian at the gates, venerable Walter Cronkite of CBS, the convention was played as an endurance test. At one point the Gipper of network news seemed to be fumbling the ball; his running commentary degenerated into a series of Porky Pig stammers. One could imagine tremors going through the CBS war machine -- Walter stammered! Walter stammered! Have the Cronkite clone ready to go! But then Cronkite recovered; "I'm trying to say . . ." he said, and then he said it.

The real hero of the day was David Brinkley of NBC, who has been anchoring conventions almost as long as Cronkite (Walter goes back to '52, David to '56) and who interjects notes of irreverence just when they are needed most. "The Republicans arriving here are so happy," he said at one point. "They're just delirious with joy . . . They are so happy it is almost as if here in this hall they were all snuggled down together in a hot tub."

Discussing the career of Joe Louis, after whom the Detroit convention arena was named, Brinkley said that eventually Joe was set upon by the IRS, "which was trying to get the last quarter he had." After a floor interview with John Connally's only delegate, Ada Mills, Brinkley observed that the woman had changed her political allegiances so many times that "she must be an emotional mess by now."

Brinkley is still solid, sharp and succinct. The best.

Of course there were goofs and fluffs; they're part of the reason convention-watching is still fun even when the convention is a charade. Chancellor had a streak of bad luck, beginning one report with the reminiscence that this was the 32nd Republican convention "since 1964 -- er, 1856." Later he introduced a snippet of Reagan interview with "Now, Gov. Reagan, on busing," only to be immediately followed by Reagan being asked, "What will you do about inflation?"

He introduced Tom Brokaw, and who pops up on the screen but a grumpy Tom Pettit, standing silently and waiting for a cue. But Chancellor could also be disarmingly direct, as when he stood on NBC's open-air balcony with Sen. Howard Baker and asked him. "Why do some of those people down there dislike you so much?"

NBC director Walter Kravetz had a knack for calling up just the right shots at just the right times, and many of the pictures NBC got were worthy of the best news photographers. NBC's camera work and technical work generally were superior by far to the other two networks', though as usual, CBS had the showiest and glitziest graphics.

All three networks seasoned coverage with little two-or three-minute nostalgia nuggets -- "A moment of History" on ABC, "Flashbacks" on CBS and "Convention Moments" on NBC. These were gambits obviously dreamed up not in news departments but in sales departments and designed to introduce excitement into the convention even if the excitement was 50 years old.

Floor reporters did their best to inject life into the show, often despite considerable obstacles. Sander Vanocur of ABC News was literally in the dark, and invisible to the camera, as he reported from the North Carolina delegation; the Republicans have the habit of frequently dimming the lights in the hall to encourage the networks to show on the air whatever piece of film is being shown to the delegates.

Cronkite went to Morton Dean on the floor for an interview with Sen. Richard Schweiker (Pa.) only to discover Dean cooling his heels while waiting for NBC's Tom Pettit to finish his interview with the senator. The CBS camera tried to keep the NBC man out of the picture and the NBC camera tried to keep the CBS man out of the picture. It's traditional.

At ABC, anchors Frank Reynolds and Ted Koppel proved about as charismatic a team as Donny and Marie, who flogged a song to death late in the evening. Reynolds continued to indulge his habit for ceremoniously handing out accolades to ABC reporters on the air, as if he were the Supreme Court of TV journalism. After a Barbara Walters interview, Reynolds said, "Thank you, Barbara. Some tough questions, and some very forthright and candid answers."

A convention that had, to put it mildly, been lacking for melodrama produced some late last week when the crowd in Detroit was, an Chancellor predicted it would be "electrified" by the appearance of Sen. Barry M. Goldwater, the Ronald Reagan of his day, which was about 16 years ago.

But when the tumultuous ovation died down and Goldwater's speech rambled on and on about Soviet threats and national strength, an NBC camera caught two gray-haired ladies sitting and chatting together and blissfully ignoring the speech, and a CBS camera spied two people fanning themselves with programs and looking bored, even as goldwater was predicting doom for all humanity should Reagan not be elected in November.

The camera caught Goldwater, too, perspiring more and more heavily as the speech wore on, until he finally, had to ask for "a piece of Kleenex." He appeared to age about a decade from the beginning of the speech to its end. It was really quite touchingly pitiful.

Bruce Morton of CBS was the first reporter to grab Goldwater after he left the podium, and after Morton finished, Walter Cronkite's voice came down from on high -- the CBS booth above the hall -- and he chatted with Goldwater as if the two were old chums. Walter said he hoped Barry would soon be flying airplanes again and Barry said if he did he'd buzz Walter's yacht in Chesapeake Bay. We viewers felt like outsiders at a geriatrics smoker.

Conflict was scarce last night, no matter how tirelessly such able reporters as Dan Rather of CBS tried to fan the fires of discontent over ERA, a subject the TV press has managed to beat into silly pulp. There was a tense moment, however when Sam Donaldson of ABC and Tom Pettit of NBC each latched onto the same delegate for reaction to the Benjamin Hooks speech. The two reporters literally asked their questions simultaneously and it was up to the delegate to decide which one to answer.

"A little traffic jam there?" chuckled Brinkley from the NBC booth.

ABC stayed with Monday morning's opening sessions for only about four minutes, rushing off just before the National Anthem so the network could illuminate viewers with a rerun of "The Love Boat." CBS filled a "moment of silence" for the hostages in Iran with the logical thing, a commercial. Only NBC carried Reagan's departure from Los Angeles live, and only NBC stayed with the podium during the official start of proceedings Monday night.

Thus NBC was most efficient at communicating the sense of event, or the sense of non-event, that goes with a story like this. It may well be that the networks will never again devote so much time, money and energy to covering political conventions, their real function in the political system having been considerably reduced, but at least NBC is both going by the book and using imagination during the last flight of the albatross.

It was a little distressing, though, to see that among the sponsors of convention coverage on underdog NBC were the embattled Chrysler Corp. (unveiling its Sinatra-Iacocca spots) and the beleaguered McDonnell-Douglas Aircraft Corp. ("Builders of the DC-10!" an announcer trumpeted). Somehow these touches served to underline just how forced the forced festivity of the whole convention really was.

At least NBC News appeared to be showing retroactive sense in cutting down on the number of appearances by Rep. John B. Anderson (R-Ill.) during the "Today Show," which is live from Detroit this week. Anderson was supposed to appear twice daily, but has so far appeared only once daily -- result of an "editorial judgment," says an NBC News spokesman -- and no wonder, what with the snappy answers he's been handing out.

Anderson on his advice for Reagan in choosing a running mate: "Well, I suppose it's rather presumptuous of me to offer any advice; it would be wholly gratuitous."

Anderson on reactions of European leaders to a Reagan candidacy: "Well, I wouldn't want to quote any of these men directly because these were off-the-record conversations."

As Carter media adviser Gerald Rafshoon chuckled last week, "I suppose Anderson is just as qualified to be on the "Today Show" as Tom Brokaw or Gene Shalit -- but maybe not as qualified as Willard Scott."

Walter Cronkite had Henry Kissinger up to the booth for a stony-faced chat, Barbara Walters, on "20/20," interviewed no less an imposing political figure than Carol Channing for a story on show biz and politics (Carol Channing?), Gerald Ford referred to "the American peeper who suffer in silence" during his roof-raising speech, a montage of scenes from his presidency was hilariously accompanied by the tune "What I Did for Love" from "A Chorus Line," and John Connally put the endless reporter questions about the Republican platform in perfect perspective when he told Tom Brokaw of NBC News, "A week from now, everyone will forget what's in that platform."