Three airliner hijackings in four days once again have thrust the Middle East onto center stage.

But the hijackings, coupled with sustained fighting between Shiite Moslems and Palestinians over the refugee camps of Beirut, are only part of a new and sustained frenzy of terrorism, bombings and confrontation, as desperate men try to fill what they see as a vacuum of purpose, if not of power, in the Middle East.

To Ali Ghandour, the weary chief of the Jordanian airline whose Boeing 727 was blown up Wednesday in Beirut, there is a reason, if not an explanation, for it all.

"Honestly, there were no demands," said Ghandour. There were no demands, at least, that the airline or the Jordanian government could meet. "It was a senseless act of senseless people who will stop at nothing."

But Ghandour also suggested a reason: "The political void in which the Middle East finds itself. The Palestinian problem and the Lebanese situation continue to defy solutions. Desperate men seem bound to do desperate things."

In the four days since the Alia Royal Jordanian Airline plane was destroyed and the terrorists escaped into Beirut's mean streets, two other commercial jets have been hijacked. One American passenger has been murdered and passengers and crew members, believed to be Americans, have been held hostage.

It is unclear whether the drama on the runway at Algiers is the act of a mainstream movement or a tiny offshoot of a splinter group of Lebanon's Shiites. Provable links to other groups with similar goals and demands are tenuous or nonexistent.

But in an Arab and Moslem political environment where national governments appear impotent to bring about change, some fanatics and fundamentalists can appeal to the roots of their societies with powerful effect. And in that sense, many of them are powerfully linked.

By making demands that may appear irrational or incomprehensible to their victims, particularly when those victims are from the West, terrorists are looking for stages where they can play on the main chords of discontent in their own societies. In some cases it appears that publicizing the demands is almost as important as meeting them.

"The stage is given to them by the airplane, by the control tower, by the press, by everybody," said Ghandour, who was born in Lebanon and has extensive political contacts in the region. "In my opinion that is why they will continue.

"But you can't prevent these hijackings by just trying to figure out how to maker better security at the airport," Ghandour said. "There must be a promise of a realizable hope of a better future."

The first great wave of terrorism and hijackings in the region came after Israel's devastating six-day defeat of allied Arab forces in 1967. The leaders of the Arab nations were humiliated, their impotence exposed. In the face of their weakness, the Palestine Liberation Organization and its various offshoots, in the name of a people without a country, found ways to demonstrate what looked like strength -- through terrorism.

Even then there was a baffling array of organizational names connected to the actions. But the situation today is even more complex. The Palestinians have, for the most part, given up hijacking as a political tool.

The terror that dominates in the region today is at the hands of groups that act in the name of fundamentalist Islamic beliefs. Many are Shiites whose sect in Iran, Iraq, Lebanon and other countries was traditionally demeaned. Since the 1979 Iranian revolution, however, they have discovered the strength of their numbers and the potential power of fanaticism.

Not all of these groups are Shiites, however, and some seem to represent the political interests of Syria or Iran as much as they do their faith or their sect. And since they identify themselves most often in anonymous phone calls to news agencies, sorting them out by name may be futile.

In the case of the TWA hijacking, some people identifying themselves as spokesmen for the shadowy Islamic Jihad group in Lebanon have claimed responsibility, while others invoking the name of the same group have denied it and vowed retaliation against media that say Jihad was responsible.

Rather than by names that anyone can claim, it is simpler to group the recent hijackers, bombers and kidnapers by their demands.

One group, which appears to include the TWA hijackers, roots its demands in the aspirations of Lebanon's indigenous Shiites. In a nation dominated by Christians and Sunni Moslems, the Shiites were a neglected minority that became, in the last few decades, a majority -- if there ever was a formal count.

They have found their political voice since the Israeli invasion three years ago, when they formed what was for a long time the only effective, relentless resistance. Their most effective tool was suicide bombings.

Various Lebanese leaders have tried, and are still trying, to become the authoritative voice for Lebanon's Shiites. Nabih Berri, leader of the Amal militia, is the most prominent politician among them, and the TWA hijackers may be part of his group or a fringe of it. The Alia hijackers appear to have ended their operation under Amal's protection.

Strident religious voices like that of Sheik Mohammed Hussein Fadlallah, leader of the fundamentalist Hezbollah, or Party of God, are also powerful. Fadlallah has often been alleged a key figure in Islamic Jihad.

Yet there is also a group calling itself Islamic Jihad that appears much more interested in the affairs of Iran and Iraq than in the domestic politics of Lebanon.

While its communiques have been issued in Lebanon, and it appears to be the group that is holding four Americans and two Frenchmen kidnaped there, its demands are aimed at the release of mostly Iraqi Shiite fundamentalists who have been held in Kuwait since 1983 for a series of bombings there.

But none of this week's hijackers have been reported to make any mention of prisoners in Kuwait.