THERE ARE EVENTS, media events, non-events and manufactured events. Tonight America turns its lonely eyes to a manufactured media non-event: the start of the new TV news season. Occurrences of one kind or another have conspired to make today the kickoff for yet another escalated phase of network competition.

NBC unveils its revised "NBC Nightly News" with Tom Brokaw as the sole anchor, the more experienced and venerated Roger Mudd having been dumped. ABC rings up the curtain on a remodeled "World News Tonight" replete with shiny new set and single anchor Peter Jennings, in New York, replacing the previous, and never successful, three-anchor format dreamed up by ABC News and Sports president Roone Arledge.

And PBS breaks a bottle of champagne tonight over the bow of its new nightly news vessel, "The MacNeil/Lehrer NewsHour," the first hourly evening newscast in network TV history. Although some PBS stations balked at the thought of surrendering another half hour of their schedules to "MacNeil/Lehrer" when the expansion was announced last spring, executive producer Lester M. Crystal says, "I think every single public TV station is going to carry us." At least during the maiden voyage.

Is this yet another new era in television news? "I don't think it's another era," says Reuven Frank, the NBC News president who has lived through several himself. "I don't think it's another era at all. It's just part of the normal, gradual, evolutionary change, brought about largely by coincidence," the coincidence being that NBC and ABC are introducing revamped programs to challenge the ratings leader, "The CBS Evening News With Dan Rather," at the same time.

And ABC's change came about at least in part because of the death on July 20 of the greatly respected Frank Reynolds, senior anchor of "World News Tonight." As indelicate as it may be to say so, it is a widely held view in the TV industry that Reynolds' death gave Arledge an excuse to change the tri-city format of his program without admitting that it has fairly consistently been a flop, and was never a very good idea in the first place.

If Arledge had put Reynolds up solo against NBC and CBS, sources say, "World News Tonight" would probably have attracted more viewers all along, particularly when the younger Rather replaced Walter Cronkite, the great American patriarch, at CBS at about the same time NBC pulled the co-anchor chair out from under veteran John Chancellor on "Nightly News." Viewers were left without an eminence, a venerability, from whom to hear the news. Many would probably have gravitated to Reynolds.

At CBS News, if there is worry, it is not spoken of aloud. One house wag says CBS should prepare promos declaring, "Our anchorman is an American and he doesn't lisp"; Jennings is a Canadian (who says "aboot" instead of "about") and Brokaw has a mild speech impediment that gives him trouble with "L" words. But this is the first time in recent history that the three evening network newscasts are head-to-head-to-head with single anchors on each, and that is bound to heat up the battle.

"It will become more a battle of stars, and more a battle of content," says Howard Stringer, executive producer of "The CBS Evening News." Stringer says viewers are more likely to pick their newscast now purely on the basis of who is anchoring it, rather than by preference of one format over the others. The formats are now essentially all the same. "Whoever slips down, or falls back, in the ratings, it will be very difficult for them to know what to do in this kind of a competitive situation," Stringer says.

CBS looks unbeatable, having not only the best of the anchors in Rather but also boasting the most formidable bench strength in all of television news. "I don't feel especially threatened," Stringer says. With their summer programs "On the Road" and "Our Times" now in uncertain hiatus, Charles Kuralt and Bill Moyers will "absolutely" be back on the broadcast, says Stringer--adding, "Thank God." The CBS first-string also includes Bob Schieffer, Bob Simon, Bill Plante, Phil Jones, Lesley Stahl, Morton Dean and Bruce Morton. Both from a competitive standpoint, and in simple terms of journalistic excellence, this lineup dwarfs the competition.

But the ratings of the network newscasts depend on many other variables besides the excellence of the program. ABC is expected by some industry observers to bounce back to first place in prime-time entertainment ratings this year, and the spillover from that success could hurt Rather and help Jennings; viewers don't like changing channels. On Channel 7 here tonight, the ABC football season begins with a Redskins-Cowboys matchup that will draw huge viewership locally, and that increases the likelihood of a sizeable tune-in for Jennings in Washington and probably in other major cities.

ABC also has a slightly different approach to the news; it personalizes stories as much as possible. If a missile were on its way to the United States, Jennings would say, "Your house may be on fire as you listen to me." They try to work in the word "you" a lot; it's all very chummy and next-doorsy. ABC News wants to lick your face like a pet puppy. Robert E. Frye, executive producer of the program, denies that this is the intention but concedes, "We do try to talk to the viewer on a one-to-one basis. We're still addressing individuals, talking to people watching a television set."

It used to be that ABC was known for its glitzy graphics and a general air of gee-whiz, but the graphics on "The CBS Evening News" are now more elaborate and showier. Stringer concedes that Arledge introduced some of these techniques but says CBS "refined and improved them." He also says he considers the other two newscasts now to be copies of his and Rather's, even to the point of using tighter shots of the anchormen. ABC moves in so close on Jennings, says Stringer, that "they're almost up poor Peter's nose." It's part of the ABC striving for a forced intimacy, and an attempt to soften Jennings' grating pomposity.

Jennings will deliver the news from a new set that has a transparent wall--"a Mercator map in etched glass," says Frye--between him and a working newsroom. Frye calls it "a very straightforward setting" in which blues and grays are predominant. There will also be a screen for Jennings to talk to when he does on-air interviews, suggesting a cross-breeding of the evening news with "ABC News Nightline" (whose ultra-able anchor, Ted Koppel, reportedly turned down the "World News" job). NBC's Frank says the set will change almost unnoticeably on the "Nightly News": "They've just kind of repositioned things so they're not quite as ugly."

Crystal says the remodeled set for "MacNeil/Lehrer" will have less of a "Louise Nevelson" depressing look to it. Sets and tight close-ups are of course mere cosmetic touches; Crystal thinks "MacNeil/Lehrer" will continue to attract more thoughtful viewers whose news appetite is not appeased by the 21 1/2 minutes they get from each network.

PBS does not have the facilities to globe-hop for stories the way the networks do, but Crystal says news footage will be bought from various agencies to add illustration to the program. Instead of dealing with one story per night, "MacNeil/Lehrer" will now deal with an average of three, "in depth, at length and in an extended and special way," Crystal says. In addition to Robert MacNeil, Jim Lehrer and Charlayne Hunter-Gault, the on-air staff will be supplemented with Judy Woodruff, former NBC News White House correspondent. A western bureau in Denver has also been set up.

Have the networks been upstaged by the fact that PBS has introduced the first hourly evening newscast, and will its existence spur the networks to go to an hour a night, as their news divisions have wanted to do for years? Frank says, "You have a fantasy that that would be true. But I don't think a realistic assessment of the impact of anything that public TV does has on people who work in commercial TV bears that out. People here don't take it seriously. It would have to be a lot better than I expect it to be for it to affect us even professionally."

Stringer says PBS is beside the point and that the obstacle to one-hour network newscasts--opposition by filthy-rich network affiliates who can make more money from their own local newscasts--is the thing that will have to budge. "Ultimately, we'll probably burst at the seams; the need for an hour news is greater than ever," Stringer says. "If you took a newscast from three years ago and compared it to one from this week, you'd be amazed at the difference. The whole pace and attitude have changed.

"Roone Arledge and CBS News president Van Gordon Sauter raised the game, and raised it again, and raised it again. So that 21 1/2 minutes is getting absurd. We've tried to do a lot of longer pieces just to prevent operating at a breakneck speed that doesn't allow a moment to reflect on what's happening. The reason people sneer at television news a lot is that, with the difficulty of getting the technology to work for you, you rush to judgment, and if you do that too much in the heat of competition, you run the danger of losing your credibility."

Thus higher stakes in the TV news ratings wars do not necessarily translate into better news for viewers. It has been estimated the networks each make at least $50 million a year from their nightly newscasts. It is the nature of the networks that no amount of profit is ever enough. Thus the pressure for ratings.

Frank says he feels no direct pressure from NBC management, but says, "There is a kind of funny gloom that develops when things aren't going well. That kind of thing. But nobody says to me, 'You better do something.' " What has changed in network news, Frank says, is that it's now not just the sales department and the network affiliates that get antsy over low ratings. "For every one on a program, from the anchor down to the copy boy, to have his juices affected by ratings is new to me," says Frank.

"I don't think it has distorted the process. We haven't done the kinds of things local stations do during sweep periods; we haven't gone to sex stories."

Frank is asked a worst-possible-scenario question: What if Brokaw doesn't work out? First he says, "I have every confidence that Brokaw will work out." Then he says he was asked the same question recently by Mike Wallace, who is helping to prepare a segment on the evening news wars for an upcoming edition of "60 Minutes." Off camera, Wallace said to Frank, "It's gonna be your ass, isn't it?" Frank recalls, and Frank said, "Yeah, sure." Then when the camera was rolling, Wallace said, "It's gonna be your problem, isn't it?" and Frank said, "Yeah, sure" again.

Frank says he also told Wallace that "CBS News is geting soft, full of stories that make people feel good instead of telling them what happened yesterday."

If Brokaw fails, NBC management has quietly hinted, Frank will be out. But he's a legend anyway; he should worry?

Frye, asked if it is not in fact the cherished goal of him and Arledge not just to lock NBC out of second place, but even to take over first, will only say, parrot-like, "My goal is to have the best news broadcast on television. How that translates any other way, I'll leave to people other than myself." Will sticky-fingers Arledge be in the booth for tonight's inaugural Jennings newscast? "I would imagine he will be," says Frye. "He's the president of this division; he can be anywhere he wants to be." Various ABC spokesmen say they don't know if Arledge will be in the news booth or here in Washington for the Redskins game.

On Friday, contemplating tonight's network news showdown, Frank said, "As a ceremonial gesture, I'm going to come in on Labor Day--late, and briefly--to make some sort of speech to the troops. I haven't done that since I was working on daily news in 1965 on the "Huntley-Brinkley Report," which Frank invented ." Then Frank thought a moment and said, "It's so uncharacteristic of me, I may change my mind and not do it at all."