ALTHOUGH THE Republican National Convention looks to be a no-surprise set-up -- a fete accompli -- there is some cause for suspense, and not over Ronald Reagan's running mate, either.

The big question is: Which network news department will emerge the winner?

CBS and Walter Cronkite, here making his valedictory anchor appearance, are naturally expected to be first in the ratings again. But ABC News could score a tactical landslide merely by coming in second. That would shatter the precedent that says in momentous or mock-momentous occurrences like conventions, ABC News always comes in last.

Spokesmen at all the networks love to insist that they don't see this as a contest, but they do. Of the estimated $45 million that each network has allocated for election-year coverage, $15 million from each goes to televise the two conventions. All three promise that their coverage will be "innovative" and "in depth" and have "a new dimension," but in general the networks differ only stylistically and in the personalities of their reporters. n

Nearly 2,000 network personnel have descended on Detroit for the big Republican live-in: 600 each from CBS and NBC, 700 from ABC. Each organization has bolstered its own line-up of commentators and floor reporters with a few guest pundits, plus the usual bric-a-brac and gadgetry. In part the contest will be between the networks, and in part it will be between all the networks and the Republican party, to see who can do the best job of not being used by whom.

But the conventions could mark a true turning point in network news -- the point at which ABC News emerges not only as the most dynamic and enterprising (and showboating) of the network news organizations, but also every bit as respectable as the two oldtimers. What could very well happen in the '80s is that ABC will become the No. 1 news network, just as it became the No. 1 entertainment network in the '70s.

For Roone Arledge, who took over ABC News in 1977, this is "My First Convention" -- something like "My First Olympics." ABC News is adopting a full-court press for the event, and its investment in promotion and advertising looks to be substantially larger than that of either NBC or CBS, with three-page ad-spreads touting the coverage in Time, Newsweek, People and TV Guide magazines.

In recent weeks, ABC's "World News Tonight" has surpassed "NBC Nightly News" for coveted second place to Cronkite in the Nielsen ratings. Now Arledge has a chance also by bypass NBC's convention coverage, even though conventions are the sort of event that usually find viewers opting for one of the two more traditional networks. This is a tradition Arledge would like to bury, yet he claims he doesn't view the conventions as ABC's chance to turn the big corner. "I think we already turned that corner," he says.

Nor does he regard the conventions as "a contest between the networks to see who has the best coverage." But on the excellent ABC News Close-Up "Lights, Cameras, Politics," which aired Friday, CBS correspondent Morton Dean referred to conventions as the "Super Bowl" of TV news. Ernest Leiser, the vice president in charge of convention coverage for CBS News, says, "It's a chance to show your people off." Gimmicks and Gadgets

Because the Republican convention is expected to be an excessively stage-managed slumber party, the networks have been busily adding gimmicks and guests stars to their plans. CBS is rushing a special edition of "60 Minutes" onto the air, and executive producer Don Hewitt himself will be among those behind the scenes calling shots during convention coverage. Bill Moyers, fresh from yet another frustrating stint at public TV, has returned to CBS News and will be on the campaign team.

ABC has not only Barbara Walters, Sander Vanocur, Ted Koppel, Frank Reynolds and other of its resident heavyweights, but also four outside commentators waiting in the wings: Haynes Johnson, George J. Will, Elizabeth Drew and Martin Nolan.

NBC has John Chancellor and David Brinkley and is hooraying over its "dramatically different anchor booths," which include open-air areas for correspondents to use for their reportage. A wag at another network laughingly refers to them as "NBC's front porches." NBC is getting more laughs, however, with its trump-card gimmick: using independent candidate John B. Anderson in "exclusive interviews" twice daily on the "Today Show" so Anderson can critique the convention he's shut out of.

"Today" will originate from Detroit, but Anderson will be on his publicity-seeking European trip, so he'll be beamed down by satellite.

When ABC News scheduled two special editions of its flashy-trashy magazine show "20/20" for convention week, Arledge says he told staff members he didn't want to see any entertainment features "like a Wayne Newton on there." Then he looked at the GOP convention schedule and "Monday night, the last hour is all entertainment! And who have they booked," he moans, "but Wayne Newton!"

Arledge also says CBS didn't schedule its special edition of "60 Minutes" (for tomorrow night at 7:30) until after ABC had announced its "20/20" plan. "That happens a lot lately," he says. "The other networks are looking over their shoulders at us for a change."

Leiser says of conventions: "The event itself has changed enormously with the rise of the primaries," he says. "These are most suspenseful events, and it taxes our ingenuity to cover them." Asked if there will be any dazzling new technological innovations this year, Leiser says, "The honest answer is no."

But Robert Siegenthaler, the ABC News executive producer in charge of operations for the convention, says the display of data will be more sophisticated than it was in '76.

"We had this computer-generated graphics machine developed for the '78 electins, but it was under-utilized then because we didn't know how to tame the damn thing," Siegenthaler says. "Later it generated flags and symbols of various nations, as well as scores and running totals, at the Lake Placid Olympics. In Detroit we'll use it for delegate counts, platform resolutions, things like that."

As a visual aid, he notes, it's a far cry from the days when convention data was hand-lettered on art cards and held up in front of cameras. But Siegenthaler says he does not know the technical name for this wonderful new contraption. "We haven't even nicknamed the thing."

ABC has built four-level anchor booths for the convention halls in Detroit and New York; images have to go through three different control rooms before they can make it to the air. Beneath the anchormen is "The Pit," where researchrs and reporters work on facts and figures to give to the on-air people.Walter Cronkite at CBS has a little man in a hole next to him to hand him cards filled with Useful Information.

Siegenthaler says ABC News also has 15 mobile cameras on the streets of Detroit to cover anything that happens outside the convention halls, and a master computer that "tells me minute-by-minute where everybody is." He refers to the entire network news-gathering convention apparatus as "a medieval siege-engine that we start up every four years." Getting Respect

The irony at ABC is that it has decided to go gavel-to-gavel with convention coverage just when everyone is saying conventions are goony birds who have outlived their era. "We are not in a position yet to be the ones to say we are not going to cover the convention," says Arledge. "Our motives would be suspect. Just like the dopes who said that we didn't carry that Carter news conference in prime time last year because we didn't want to lose money on entertainment shows. Well [ABC TV president] Fred Pierce and [ABC Inc. president] Elton Rule were the ones who thought maybe we should carry the president. I'm the one who argued against it."

Arledge is still a little touchy about criticisms which say ABC News is gaudy, circussy, cheap, sleazy -- well, you know. Are Arledge's First Conventions a chance to get increased respect for ABC News? "I suppose, in a way. But I think most people respect ABC News now. Maybe certain parts of certain programs are not as respected, but there's not the feeling that there used to be that ABC News was not a serious news organization.

"I really don't understand what people are talking about when they say we're jazzing up the news. CBS is using all kinds of effects and things on the air. NBC has music and chimes and 'Coming Up' on 'Nightly News.' We just try to get in as much information as we can.

"Believe me, I literally did not turn down three or four extremely lucrative offers so I could come in here and shlock up the news."

Arledge still thinks he's a victim of "certain preconceived notions fueled by some of the early dumb things we did," but -- except for the escapades of Geraldo Rivera and his vigilante journlism -- ABC has become a first-class news operation, and it probably does a better job of exploring the technical possibilities of television than the other networks.

And so, even if ABC News doesn't "win" in the coinvention ratings, we may see a decade of ABC News leadership being ushered in. Arledge does not find this hard to conceive.

"CBS News will have a new president a year from now. I would guess they think they've got a winning formula, so there's impetus to change. They'll be weakened with Walter Cronkite leaving. Rather will do well, but anchoring is not his No. 1 strength. NBC is in the process of constructing a mini-CBS right now, so those two networks are going to look very much alike. We'll offer an alternative that people will find attractive."

There is nothing whatever farfetched about this prognosis. If anything, it's a conservative view. NBC News is not in great shape right now, and though Roger Mudd has indeed been hired (along with umpteen other CBS people) by CBS alum and NBC News president William Small, the "Nightly News" is still in the hands of the increasingly professorial John Chancellor, so professorial he now insists his name be pronounced "Chan-Sell-Or." CBS News has a lame-duck president in William Leonard, who must retire by chairman William S. Paley's mandate next year, and about all he has time for now is to keep closing the barn door after another horse has bolted out it.

Arledge emphasizes he doesn't look to the coventions as the decisive factor.

"Huntley-Brinkley 'won' in 1956, and suddenly NBC was No. 1 in news, but that sort of thing doesn't happen any more. I'm not downplaying the conventions as news stories, but I don't think they are the criteria by which you judge a news operation that they once were. I think people now look at the totality of coverage."

Arledge says that "if I didn't feel we had to make up for the fact that in the past ABC has not covered the coventions adequately, we wouldn't be giving them as much time as we are."

Of course Arledge himself expects most viewers will watch CBS News because this year's convention marks -- sniff, sniff -- Walter's Goodbye. Indeed, CBS is promoting the conventions not as political rites so much as the nation's farewell to Walter Cronkite, the grandfather clock of American journalism who will be winding down and anchoring his last. Yes, we can see all the politicos making pilgrimages to his booth to bid his, oh, not goodbye but perhaps, au revoir!

But lest we forget, Cronkite is one of television's most accomplished communicators and has been anchoring conventions since 1952. CBS reports solemnly that "when the last gavel sounds in Madison Square Garden in New York City on Aug. 14, Cronkite will have anchored more than 450 hours of convention coverage for CBS News and the CBS Television Network."

Don't be surprised if ABC News and NBC News end up interviewing him.

Of the media verities that may come out of these conventions, one is that gavel-to-gavel coverage -- in a new day of primaries and caucuses -- could be headed for the attic with other antiques. Conventions are becoming about as meaningful to the political process as the Ice Follies.

And in 1984 (the year, that is)?

"I wouldn't venture to say," answers Leiser of CBS. "If there's not a change in the construction of the primaries, if the conventions are just going to be annointment proceedings, then we'll have to review the idea of having extensive coverage."

Eras end all the time nowadays, but starting tomorrow, we may be able to witness yet another one noisily and glitteringly bite the dust.

Over to you, Walter.