CBS News correspondent Tom Fenton was finishing his stand-up report near the American Embassy in Tehran when demonstrators began crowding around the camera crew. He thought things might get out of hand when suddenly a demonstrator rushed forward to ask him, "CIA?"

"No," Fenton replied quickly. "Cbs!" He and the demonstrator, and many in the crowd, broke up laughing.

It was another little irony in a situation riddled with paradox. The capture of American hostages in Iran has moved well into its second month and become television's first, live, Global Crisis Mini-Series. Depending on its outcome, it may be anything but the last.

NBC News president Bill Small says one of his producers recently moaned, "I look forward to the day when our lead is not Iran," but no one knows how far off that day is. The sight of chanting, fist-waving mobs has become part of the fabric of everyday lives for millions of Americans through TV, and one can't be blamed for wondering if some dank new age has now been ushered in -- an age of Terrorvision, in which the term "air power" takes on an entirely different meaning.

Last night's NBC News interview wit Marine Cpl. William Gallegos of Pueblo, Colo., taped earlier in the day at the U.S. Embassy, may have been the most powerful broadcast yet out of the heavily televised trouble spot. It was the first chance for American viewers to see one of the hostages in captivity, and it made an uncommonly compelling 18 minutes of grim reality television.

Although Gallegos did not appear visibly traumatized, the sight of him suddenly personalized the story as it had not been previously. "The students here have been really good to us; it's hard to believe, I know," Gallegos told two NBC reporters in an embassy room dominated by a poster of the ubiquitous Ayatollah Khomeini.

The Iranians were operating the cameras, which occasionally panned to lingering shots of anti-shah posters, particularly during a five-minute harangue by a spokeswoman identified only as "Mary."

NBC News could have edited the interview, a spokesman insisted last night, but chose, on the advice of correspondents in Tehran, to run it in its entirety. This left the natural tense rhythms of the session intact and made the broadcast all the more gripping, if all the more bizarre, a spectacle.

The network had planned to air the interview at 9 p.m., and promoted it heavily with the sensationalistic title: "Hostage! The First TV Interview." But at the appointed hour the spectre of debacle loomed; correspondent John Chancellor told viewers the satellite feed from Iran was "delayed because of technical difficulties."

He also said the difficulties could be "not technical but political," and that Iranian authorities might have decided they didn't want the interview seen. But it finally came on the air at 9:46.

An NBC News spokesman said immediately after the broadcast ended at 10:14 that there was no evidence of sabotage and that it was being assumed the problems were accidental. Chancellor was quick to point out to viewers, following the interview that it left many questions unanswered and contained contradictions and inconsistencies with what had previously been learned about the hostages and their treatment.

But as is so often the case with television, it was not so much what was said as what was seen and perceived that gave the interview its impact.

NBC News officials defended concessions they made to the Iranians, in order to get the interview, with remarkable consistency. An NBC News spokesman said yesterday that the statement made by "Mary" helped demonstrate the "intensity and depth" of Iranian feeling. Later, Small said the statement would show the "intensity and depth" of Iranian feeling.

And finally, on the telecast itself, Chancellor spoke of the "intensity and depth" evident in the statement.

Newspapers are certainly represented in Iran as well, but television and its dramatic pictures have brought the living story into the American living room. The White House and State Department aren't seeing a lot of this stuff even one instant before it is made available to millions of American viewers.

What viewers often see are huge crowds of Iranians demonstrating their hatred for the United States, and yet if there weren't official Iranian cooperation with U.S. TV networks, those pictures might never cross the Atlantic. And network news personnel stationed in Iran have, for the most part, felt little threat to their own safety.

"I wouldn't rate it as a very dangerous story," says Fenton, now in London after three weeks in Iran. "It's a problem of the cultural gap. Americans don't realize its's just Persian hyperbole when the crowds chant 'Death to Carter.' They're not ready to slit the throats of Americans by any means.

"At the same time, the Iranians don't understand Americans. They have absolutely no idea how furious Americans get when they see their flag burned or their president hanged in effigy."

The Iranians are, literally, sending out a signal, one that literally goes over the heads of official diplomats -- by satellite. Each day the networks get 2 1/2 hours of satellite time via the state-controlled VBIR, "Revolutionary Broadcast Center." With some exceptions, this operation has been running along swimmingly.

"They have been edgy and shoved some people around," says Ernest Leiser, CBS News vice president, "but they are dying to get their message across." In this age of instant communication, exposure is power and access is politics.

The Iranian television show isn't being produced purely for the consternation of Americans, either. Demonstrations are also covered by Iranian TV. Not for nothing was Sadegh Ghotbzadeh promoted from head of the Iraniana television authority to foreign minister -- a move roughly comparable to a U.S. president naming Fred Silverman secretary of state.

Yesterday in Tabriz, pro- and anti-Khomeini forces battled for control of a central power source: the television station. Air Time Is Power

Meanwhile, how do the American networks know they aren't being used by the media hip Iranians? "We don't want to be used by them, but we still want to get every tidbit we can about everybody," says Robert Siegenthaler, director of special events for ABC News.

"These people are tremendously media-conscious," Siegenthaler says. "The Revolutionary Council are like cheerleaders with bullhorns, and they bring out the demonstrators -- truck drivers one day, ladies and self-flagellators the next -- and so we try to keep using words like 'orchestrated' and 'well organized' so that we're not being a kind of mindless mirror. We are trying not to be victimized."

The object all sublime is to get on television, to make that direct entry into American -- and Iranian -- homes and minds. No one in TV journalism quarrels with the idea that the Iranians are trying to use the press -- only with the suggestion that they are succeeding. Some of the attempts at manipulation are as rude as this: ABC News personnel have been approached by strangers claiming to have secret tapes of the hostages taken inside the embassy and offering them for sale. It's on a level with the porno trade and "no one has bought the Brooklyn Bridge yet," says Siegenthaler.

Fenton says the students are getting so "savvy" about TV exposure that they have offered him "secret government documents" in exchange for "five minutes of unedited air time." Time may be money, but Air Time is power.

Finally, this weekend, after two more offers the networks all felt they could refuse, NBC News came up with a counteroffer; they got the Gallegos interview in return for giving a militant Iranian a few minutes to state her case on prime-time television. At CBS News, NBC's move was looked down upon as a capitulation to manipulation.

But NBC's Small said, "If I were at one of the other networks, I would like to have this myself. We think it is a terribly important public service to present the first interview with a hostage in the embassy. I'd hate to think someone got so righteous as to say we shouldn't do this. We need all the insights into this situation that we can possibly get."

Small said that although Iranian representatives were present when the tape was edited in Tehran, they had no say over how it was edited. The "Tonight Show" was canceled and a one-hour late-night analysis scheduled, Small said, to make it clear what the circumstances of the broadcast were. "I don't think our viewers are going to be fooled," he said.

As usual, pro-Khomeini Iranians in the United States were undoubtedly monitoring the NBC newscasts and reporting their reactions to the folds back home. Let's say the Iranians are very image-conscious -- so much so that CBS News was briefly denied access to the satellite on Friday because Iranians here took offense at remarks made earlier in the week by writer Carl Rowan on WDVM-TV, the CBS alliliate in Washington.

CBS was about to send back a report on anti-Khomeini demonstrations in Tabriz when the Iranians pulled the plug on the satellite. It took "hours" of haggling to get back the bird, a CBS News source says.

By insider's estimates, each network has already spent between $500,000 and $750,000 covering the Iranian crisis, Expenses in Tehran alone amount to $75,000 a week for each network. Unanimously, network news executives say the public is rewarding this effort with lavish attention. ABC News, which has been the leader in the amount of Iranian coverage broadcast, has found that its late-night reports have on occasion out-rated entertainment programs on other networks, including NBC's "Tonight Show." TV Strategy'

Even if State Department spokesman Hodding Carter III hadn't brought it up -- and infuriated the networks -- with his recent remarks, the question of where coverage ends and participation begins would naturally have arisen during this story. No one complained much when it appeared that Barbara Walters had helped talk Sadat and Begin into a powwow for peace during the media blitz on the Mideast in 1978.

But in a situation as fraught with potential calamity as the Iranian crisis, there is natural concern that TV's penchant for participatory journalism could endanger lives or prolong the ordeal.

Ed Fouhy, Washington bureau chief for CBS News, thinks such talk is just idle steam. "That TV diplomacy' stuff is nonsense," Fouhy says. "It's untrue. It's a base canard. I'm inclined to use the old Fred Friendly answer: Colonials threw tea into Boston Harbor, and there weren't any cameras there."

"We are not negotiating -- far from it," says Fenton of CBS. "But we are looking for anything that might be an opening. You couldn't help feeling that if there was anything that looked like a possible compromise, it was worth promoting."

ABC's Siegenthaler rejects Hodding Carter's notion about the ayatollah allegedly hardening his line during the network interviews; "I don't go for that at all." But Siegenthaler did say that covering a situation in which hostages have been taken does bring up its own set of problems -- a set of problems the world may see a great deal more of in the electronic '80s.

"In the mid-'70s, when we had the Moluccans and the Hanafis, we went through a whole set of jazz about how do you deal with a hostage situation," Siegenthaler says. "Deejays were calling the Hanafis inside the buildings they'd taken over, and all that. The thing is, no general set of rules applies to every situation.

"We can't consider suppressing the news, or lying doggo, or only reporting what the police tell you. It's a terrible, thin line to walk, and sometimes, I guess, we stray."

"One of the most disturbing things to the press over there is when correspondents are accused of trying to negotiate," says Walt Garrity, an NBC News unit manager who just returned after 15 days in Iran. "It's an injustice. Because they ask a question doesn't mean they're negotiating. The government emissaries couldn't get in, anyway."

This line, however, leads inevitably to other conjecture: Would the tactics being used by the Iranians ever have been considered if television's global link-up weren't there to beam the message back to Americans? If TV strategy is part of the Iranian plan, isn't television a participant no matter how hard it tries not to be?

"The funny thing is, we had so much trouble getting into Iran a year ago, and you couldn't even get near that TV station," says Burton Benjamin, director of news for CBS News."But now there's no trouble. Obviously they want their message to get out."

And NBC's Garrity says, "We had a nice relationship with Iranians. They like Americans over there.The people feel wronged by the United States and various administrations, and they'll shake their fists and shout 'Death to Carter' at you, and then they'll smile and tap you on the shoulder. 'They have an honest liking for the American people, and some of them are damn decent to talk to."

News executives will not talk on the record about how this attitude might change should worse, as it has throughout world history, come to worse. There is talk of a civil war in Iran that might endanger the press along with every other American. Privately, government sources not that even if there were a way to free the hostages, that would still leave 100 American journalists now headquartered at the Intercontinental Hotel, which militant students roam at will.

"No one wants to think what would happen if there were a rescue attempt or some kind of punitive action taken," Siegenthaler says. The Coverage Continues

It's ABC that has played this story the heaviest, with more hours of special reports than the other two networks combined. ABC has even prepared a fancy electronic logo for each report: "American Held Hostage," the program is called. All three networks are now ballyhooing their coverage with promotional announcements, each implicitly claiming that the bad news is better on one network than the others.

In addition to the overseas crews, network news departments are maintaining 122-hour shifts of crews at the White House, State Department and, now, at the temporary residence of the shah in Texas.

There is no sign that the American people are tiring of the coverage.

The only way we have to measure that is audiences," says Leiser of CBS, "and ours and ABC's are huge. We're getting a 13 rating at 11:30 at night and that's only a couple of points behind the evening news."

ABC has promised nightly reports as long as the situation in Iran "remains critical." At the other networks, this is quietly considered more a matter of showmanship than journalism.

"There's not a story to do every night, no," says Fouhy of CBS News. "To commit in advance, not knowing what the news will be, is obviously overkill."

If ABC's approach may be unprecedented, so is the news story. Even if there were no other positive side to the crisis, Americans are learning more about the temperaments, politics and geography of the Islamic world than they have ever had a chance to learn before.

"We're getting very good feedback," says ABC's Siegenthaler. "There's a technical crew in Detroit that stays on after the local news at the affiliate there just to watch our Iran shows. To know as much as possible can only be good for people. If they see the situation reported with all its nuances, I think there is less tendency toward jingoism and xenophobia."

And Iranians on the streets of Tehran seem determined that Americans will know "as much as possible" about their side of the stalemate. Fenton says it was not uncommon for Iranian pasers-by to offer him and his crew advice on camera angles, help set up the tripods, even help plug in the video cameras. "We are part," he says, "of their game."