A long national television nightmare ended with a long national television daydream. Yesterday was the Fourth of July on network TV, a day of triumphal marching, waving crowds, patriotic tunes (even "It's a Grand Old Flag" by George M. Cohan) and a ceremonial social on the White House lawn.

The Iranian hostage crisis went out in a blaze of cathartic, nostalgic, telegenic excess. Network news personalities jettisoned any pretense of cool objectivity and all but joined hands to trill a few choruses of "When Johnny Comes Marching Home."

The freed hostages had their day in Washington and probably their last day together as a group on nationwide television, the medium from which most Americans first learned of their capture and through which countrymen and statesmen alike learned many of their personal characteristics and followed their plight for 444 days of confinement.

Now it was Day 8 of their imprisonment in the Public Eye.

"I hope you were watching TV," said charge d'affaires Bruce Laingen to President Reagan on the South Lawn of the White House during ceremonies there. You had to be watching TV, Laingen said, in order to appreciate fully the warmth and fervor of the welcoming crowds that lined the former hostages' bus route from Andrews Air Force base to the Capitol and down Pennsylvania Avenue to the White House.

Actually, you had to have been watching TV for the past 14 1/2 months to know this crisis, and to know by sight a cast of characters who made their way into the same part of the American consciousness that houses J.R. Ewing and other residents of "Dallas," the doctors and nurses of "M*A*S*H" and the personalties of the network news people covering the story. The crisis contained its own new array of household faces -- the prim and straightforward Elizabeth Swift, the nervous Cpl. William Gallegos, the abidingly stalwart and dewy-eyed Louisa Kennedy.

Yesterday was a day made for television -- from such sights as the hand-lettered "thank you" sign held out a bus window by a hostage as the caravan moved through the crowds, to President Reagan patiently waiting out the protracted Army ceremonial maneuvers in his back yard starting to hold his hand over his heart for the playing of "Hail to the Chief" and then saying suddenly, "Oh! I thought this was the national anthem."

And the day brought to a crescendo a crisis made for television. Some say -- and will be arguing the point for years to come -- that it was a crisis made by television, at least the new globe-shrinking satellite kind of television that gave Iranian militants a virtually open line and direct access to American citizens.

TV journalists found it part of their role to get openly caught up in the story that had turned some of them into extremely familiar faces. Of the hostages, Ted Koppel of ABC News -- which more than any other news organization had made the story its own -- said early in the coverage yesterday, "They are all heroic and they are all very much entitled to this day of celebration they are going to get."

When it was over, Koppel said, "It was a glorious day of ceremony." Roger Mudd of NBC News declared, "This has been a sweet day for America." Dan Rather of CBS News exclaimed in the tight-lipped way he exclaims things, "What a memorable afternoon . . . There is no need to think of anything profound to say." And he didn't, either, choosing instead to misquote from "The Wizard of Oz."

The Rather version: "Gee, it's great to be back home." The actual line: "Oh Auntie Em, there's no place like home!"

But network correspondents really didn't have to stretch very much to give the events and remarks of the day the plush luster of fiction. Even the West Point press conference with began the day had an aura of fantasy about it. Here were the long-lost (41 of them anyway) propped up in rows on a stage, so resembling a game show gallery that wags quickly dubbed the program "The Hostagewood Squares." Laingen said, "I don't want to dominate this show in any way," but he spoke for 10 minutes at the beginning of what had been announced as only a 14-minute dose of exposure.

There was playful kidding, as when one Foreign Service officer directed another to tackle a question about whether the shah should ever have been allowed into the United States in the first place. There was the virtually inevitable disruption from the back of the room; a woman announced she was daring to ask how the hostages could spread "hypocrisy" about torture when the CIA had such a nasty record on this score, and so on, until she was drowned out for being a party-pooper.

And there was the all-American, latter-day-Andy-Hardy note sounded by Marine Sgt. John McKeel who said he wanted to "get back to chasin' women."

"I was struck with just how truly remarkable this entire scene was," gushed NBC News correspondent Bob Jamieson, but colleague Linda Ellerbee had the moxie to note that it had been "a very controlled scene," and that Lanigen had talked too much. She also seemed disappointed that no new torture tales had come out of the press conference.

Throughout the day, coverage of the events was interrupted on the networks by commercials for, among other things, the National Star newspaper -- a depressing reminder that soon the hostages will pass out of the realm of network news coverage and into the pages of supermarket tabloids; it's like an evolutionary chain.New stories of torture and abuse, real or trumped up, will probably chase alleged occult encounters between Yoko Ono and the late John Lennon right off the front pages.

Network newsers apparently felt so close to the story that they assumed the additional roles of populist cheerleaders and spokesmen for the Folks At Home. "We appreciate what you did for your country," Dan Rather told hostage negotiator Warren Christopher after a brief interview. Later he told visiting sage Eric Sevareid, "If I'm any judge, and frequently I am not . . . the American people for a long time have had a yearning to feel good about something."

The network correspondents decided, almost unanimously it appeared, to wallow in the good feeling for all it was worth. Lesley Stahl of CBS News even proposed that "perhaps the Vietnam era is over at last for all of us." Stahl also declared the arrival of the hostages comparable to the triumph of the American hockey team at the 1980 Winter Olympics.

John Palmer of NBC News told viewers, "I feel personally very privileged to have been here," covering the events at the White House.

But it was Rather -- throughout the day diamond-bright and diamond-hard in his reportage and narration -- who bothered to briefly consider "serious questions that all of us journalists have to ask ourselves about how we covered this story . . . particularly in the early stages. . . But," said Rather, "that is perhaps a subject for another day."

And ABC's Frank Reynolds and Ted Koppel took at least token pains to recall that Vietnam prisoners of war, many of whom had spent much longer times in much more severe confinement, were not accorded the kind of jubilation and hoopla that swept through Washington and, via TV, the nation yesterday.

Cameras were also heroes yesterday, picking out irresistibly emotional shots of homecomings and reunions at Andrews. "We're not going to lose track of that pretty girl," vowed ABC's Reynolds of one young women whose nervous yearnings had been highly visible as the plane touched down and who finally rushed forward to hug ex-hostage Rodney Sickmann in a finale fit for the warmest and toastiest of Pepsi-Cola commercials.

Indeed this was a day filled with images of live and spontaneous Americana that usually show up only in cunning simulations designed to sell products and the feelings they allegedly engender. This was no product. This was the real article.