IT'S CRAZY, but Teddy Kennedy never looks quite so presidential as when he is declaring that he is not a candidate for the presidency. The senator's brief press conference announcing his withdrawal from consideration for the 1984 Democratic nomination, carried live by all three networks yesterday morning, was a little lightning bolt of television and yet another memorable installment in the ongoing Kennedy Saga.

"The Kennedys" -- it's one of America's great continuing real-life serials. It has everything. As a source of fascination, it's even better than the Richard Nixon Story, because while Nixon has been living out a madcap, agonizing and sometimes infuriating political life on the itty-bitty screen, it was never a family saga, like "Dynasty" or "Dallas." It was just Dick Against the World -- always entertaining, but never quite an epic.

Those who have been faithful to the Kennedy story, and it's awfully hard not to be -- it's high-stakes gossip, of equal appeal to tabloids and to proper journals -- must have noticed yesterday how remarkably assertive, candid and purposeful Kennedy was, in contrast to the tongue-tied, hesitant Kennedy that people remember from Roger Mudd's 1979 CBS profile, "Teddy," one of the pivotal political broadcasts of all time.

He was so good that he seemed to render the attendant press corps all but speechless. Teddy didn't stumble over his words; the reporters asking questions after his statement did. They got spooked by royalty as reporters are occasionally wont to do -- even though this was royalty who'd been pretty generously kicked around by many of them.

Perhaps the most impressive thing about the Kennedy appearance was that it may have been one televised political moment that was exactly what it appeared to be. It wasn't a soft shoe. Sen. Kennedy said he was withdrawing for family reasons -- his three children sat telegenically nearby -- and according to one source close to the Kennedys, the children actually voted on the decision, three-to-nothing against running.

Maybe politicians are naturally at their best on television when they are telling the nearly unvarnished truth. It happens so seldom that when it does, it's breathtaking.

Indeed, NBC's Senate correspondent John Dancy said on the air, after the press conference, that there were still questions about Kennedy's "real reasons" for withdrawing, and ABC News correspondent Brit Hume was visibly forcing himself to accept the notion that a politician had actually said what he meant.

The irony was not lost on observers that when Kennedy was seeking the presidency in 1979, he came across poorly on the air, but when he was renouncing it yesterday, he was splendid.

Why the perplexing difference between Old Teddy and New Teddy? "He was never entirely comfortable with the 1980 race. He was never able to develop a rationale for his candidacy," said the Kennedy source. Kennedy is one of the few powerful orators left in the Senate, but oratory doesn't always translate into effective television. It did with the "dream shall never die" speech at the 1980 Democratic convention, but prior to that, Kennedy's campaign appearances on TV were often clips of him speaking before inflamed crowds. The crowds went wild but the performance was too shouty and intense for TV.

As in romantic novels, some characters from past chapters of the Kennedy saga re-appeared for yesterday's announcement. CBS Capitol Hill correspondent Phil Jones, who had seemed the spiritual leader of the Get Teddy movement of 1980, asked a relatively docile question from the floor. And Mudd, now Washington anchor of the "NBC Nightly News," anchored coverage for NBC.

"There's nothing like being in Washington when a surprising major political story breaks, and that's what's happening this morning," the politically savvy Mudd told viewers, gleefully. His last words on the NBC broadcast were, "It's fun to be in Washington today." Indeed, there is good reason to be selfishly saddened by Kennedy's announcement from the armchair-pundit point of view, because it virtually guarantees that the 1984 race will be less interesting to watch on television than if he had been part of it.

Thus are some TV political junkies in great despair that Jerry Brown lost his Senate bid in California this year. He may be a jerk, but he would have made for sizzlingly entertaining TV, albeit perhaps of the sitcom stripe. Washington would look so lively and vital on the air.

Reporters wanted to know who the next logical front-runner for the Democratic nomination is. The question should be, especially during the reign of President Hollywood, who is the next most telegenic Democratic hopeful? All the Democratic hopefuls have signed up television advisers to turn them into scrumptious and delicious TV personalities. John Glenn is considered the front-runner in this regard, but he has a lot to learn. At approximately this very moment, he is trying to learn it.

ABC News was the first network news organization to decide to go live with the Kennedy press conference, partly because it was apparently the first to learn there would be one. David Burke, an ABC News vice president who once worked for Kennedy, phoned the senator Tuesday night after hearing of a Boston Globe story on Kennedy's plans to withdraw his name, and Kennedy told him about the press conference then.

NBC News, however, says it was first to announce the Kennedy decision on TV, at 8:58 Tuesday night, on an "NBC News Capsule" with Linda Ellerbee. CBS was able to get mention of the story into the West Coast update of its "Evening News With Dan Rather" show, at 9:36 Eastern time.

It's ABC's entertainment side, meanwhile, that is defying what ought to be a television axiom: Never try to improve on a reality that everyone has already lived through television. ABC now has in development an eight-hour mini-series, "The Kennedys of Massachusetts," reportedly covering the family from 1863 to 1963, for airing in the 1985-86 season. Teddy Kennedy will be 54 that year, and no doubt raring to run. How does ABC think some dumb mini-series will be able to tear us away from the real thing?