Strike a deal with the hostage-takers as promptly as possible. Or shut off all contact with them until they release the Americans.

On television the other morning, Zbigniew Brzezinski was proposing the first course of action at the very moment that Henry Kissinger, on another network, was arguing for the second. As the hijacking of Trans World Airlines Flight 847 drags on into Day Seven, a legion of experts has been crowding the airwaves to urge everything in between.

If all of this contradictory advice leaves average Americans baffled, it also points up the ephemeral unknowns of crisis negotiation. Although professional negotiators and academic theorists have proliferated in the past two decades, along with terrorist acts, the skill remains a delicate blend of seat-of-the-pants science and almost-art.

"The beautiful part of negotiating in a stream of continually changing streams," says New York lawyer Gerard Nierenberg, founder of the Negotiation Institute, "is that there are many, many thousands of alternatives to use. The temptation is to try to only use our same success patterns over and over again. But the success pattern of the last negotiation is often the worst way to go in the next one."

One problem is that short of negotiating in earnest, there is no reliable way of learning how, says Algerian Ambassador to the United States Mohamed Sahnoun. His government, which helped obtain the release of the American hostages in Iran 4 1/2 years ago, has assumed an on-again, off-again role in the present episode.

"Most people who think they are experts in negotiation have not been negotiating themselves," says Sahnoun. "I have attended some of these seminars on conflict resolution. I notice that many people have very excellent theories based on social drama and psychodrama but that very often the deductions are not adequate. They miss the human touch."

As his country's ambassador to West Germany in December 1975, Sahnoun helped gain the freedom of seven OPEC oil ministers kidnaped by pro-Palestinian terrorists at OPEC headquarters in Vienna. As for the Shiite Moslem hijackers, who insist they will hold the 40 Americans in Lebanon until Israel releases the more than 700 Shiite detainees, Sahnoun offers the following negotiating advice:

"You should take a comprehensive approach without giving in. If you give in right away you have no leeway. One should not be very impatient. It's very, very tense, and a complicated psychological problem. You have to understand what is behind the rhetoric -- what is essential for them and what is rhetorical. And you have to know when they have to save face. You have to know when they are too sure, too confident of themselves. You have to know what the negotiator on the other side is going through."

Says career diplomat David Newsom, a professor at Georgetown University, "The important thing to realize is that terrorism, however much we may dislike it, has its own particular logic. In this sense we're dealing with people who see us as one of their principal adversaries."

He allows that a successful negotiation requires each side to understand the "political realities" of the other. "That, I think, is the heart of the process. People like these young Shiites in southern Lebanon know very little about how our country functions and how the decisions are made. And perhaps we don't know their political realities.

"The other thing I think is important, and perhaps this can be done through secret channels, is for the United States to make clear the limits of its tolerance. The Carter administration sent a message to the Iranians that any harm to the hostages or placing any of them on trial could lead to certain specified consequences -- and the hostages were not harmed or put on trial."

The current situation has been further complicated by the declared U.S. policy, restated by President Reagan yesterday, of never negotiating with terrorists. Some experts raise the question: Is it possible to negotiate without negotiating?

"I think it's kind of ridiculous, chest-pounding machismo to say we are not contributing to any arrangements," says Brzezinski, who as President Carter's national security adviser was intimately involved in the Iranian crisis. "I don't care if the word 'negotiation' is used. I see no reason why we cannot contribute through de facto negotiation . . .

"My view is that before a situation completely jells and becomes increasingly overloaded with extraneous and additional demands, it is better to cut a quick deal after a kidnaping even if it means some concessions. I fear that if rapid movement is not made, it'll get worse. In the longer haul, the demands of the kidnapers will escalate and become more extraneous."

Asked whether the Greek government's release of an accomplice early on in the hijacking has weakened the American negotiating position, Brzezinski says, "I don't even want to talk about the Greek role in this because it is so disgusting."

These views notwithstanding, social anthropologist William Ury, director of Harvard's Nuclear Negotiation Project and author of "Beyond the Hotline," a book about crisis control in the nuclear age, says, "The record shows that the longer you talk, the longer you hold the hostages, the safer the hostages are. At the same time, it's important not to give in. If you do that, then they'll simply learn that the best way to do business with the U.S. is to seize a TWA airliner.

"You want to kind of fudge the situation. The hostage-takers want to make things very clear, with a very clear deadline, but we should want to stretch things out, make it all unclear and keep a low profile. Americans are the most impatient people on earth, culturally speaking. Given all the media attention, the situation seems increasingly intolerable. We need to hold ourselves in check and to realize that we need to give these people some more time. In other words, we should hunker down."

In the meantime, Ury says, "We should make it clear to the hijackers that we're a huge, powerful nation and we're not going to have our entire affairs of state turned astray to react to pinpricks."

Another Harvard negotiation expert, law professor Roger Fisher, coauthor with Ury of the best seller "Getting to Yes," argues that the United States should persuade Israel to release its Shiite prisoners -- illegally detained, in his view -- in exchange for the release of the Americans.

"It is not appeasement to pay your debts," he says. "It is not submitting to blackmail to do what you ought to do." He says such items as money and jewelry stolen from the hostages could serve as bargaining chips in the talks. "And we should invent some options of our own . . . People tend to decide first and talk later. I think we should talk first and decide later."

And as for proof of his bona fides, Fisher says, "When I got my Toyota, the dealer told me I got the lowest price ever."

"Roger Fisher is brilliant, but whenever somebody says that after a negotiation, you know you got screwed," scoffs Chicago negotiator Herb Cohen, author of "You Can Negotiate Anything." "We're dealing with tough, cynical people, okay? And these other guys? They went to Hotchkiss? They went to Harvard Law School? The London School of Economics? These are all wonderful criteria for dealing with a mullah."

Cohen, director of Chicago's Power Negotiation Institute, says the United States should use an intermediary such as Algeria. "The worst person who can negotiate for you is you." Of the terrorists, he says, "Don't play by their ground rules. These are the classic rug merchants. This is a big sellers' bazaar."

He also counsels patience, consistent argument, and disciplined focus. "Don't get sidetracked into a discussion of Shiite grievances. Keep the focus on the main issue -- the American hostages."

And proceed, he says, with extreme caution.

"The biggest problem we have right now," Cohen says, "is where does the locus of power lie? Does Shiite militia leader Nabih Berri speak for all the hostage-takers who have captives? I have a feeling that he may not. That makes the situation dangerous. If we move fast to negotiate with Nabih Berri, we may find we've been dealing with the monkey when we should have been dealing with the organ grinder."