The presence of a high-ranking Syrian intelligence officer in West Berlin early this year and alleged Syrian involvement in an attempt last month to blow up an El Al airliner have touched off a sweeping reexamination by western intelligence agencies of Syria's role in supporting terrorism.

Allied investigations into terrorist incidents in Britain, Italy and West Germany are leading European authorities to the conclusion that Syrian intelligence has been far more involved than previously suspected in abetting Arab terrorists in their operations in Western Europe.

But most western governments still seem to believe that Syrian President Hafez Assad did not directly order or approve of either the recent attempt to blow up an El Al jumbo jet or the bombing of a discotheque filled with American servicemen in West Berlin.

This tentative conclusion about the Syrian role in terrorist incidents in Western Europe is not totally shared, however, by all Reagan administration officials, who seem to be sharply divided in their evaluation of the "Syrian connection" to terrorism in Western Europe.

The El Al incident, widely viewed as a probable trigger for a massive Israeli strike against Syria or Libya had it succeeded, has nonetheless served as a powerful catalyst for a total reevaluation by western intelligence services and antiterrorist experts of the current Syrian role in terrorism.

Even those U.S. officials most reluctant to pin responsibility for the El Al bombing plot on Assad regard the extensive evidence of Syrian links to the aborted attempt as "new and very disturbing" evidence of Syrian support for terrorism in Europe.

That evidence includes a close relationship between Syrian intelligence and the Jordanian arrested in London for attempting to blow up El Al Flight 016 on April 17 as well as with his brother, who has confessed to bombing an Arab-German club in West Berlin March 29 with explosives provided by Syria's embassy in East Berlin.

One Pentagon source noted that the El Al plot came close to succeeding, the bomb having been found only on the Israeli security officials' third search of the luggage of the Irish woman who was unwittingly carrying it. Had the 10 pounds of explosive gone off in midair, almost every clue to those responsible most likely would have vanished in the wreckage, he said.

This source, familiar with the details of the British investigation, said he was convinced that Assad must have known about the El Al plot beforehand and believed it was so well conceived that the risk of its being discovered or linked to Syria was minimal. The Pentagon source did not, however, provide any details to corroborate this impression, and refused to be identified.

Western European officials and a Pentagon source also suspect that Syrian Air Force intelligence officers with close ties to Assad were the masterminds behind the attempt to place a bomb aboard the El Al plane.

Syrian "Handling?"

Some U.S. and Western European antiterrorism experts believe that Syrian Air Force intelligence was directly involved in "handling" both brothers, Nezar Nawaf Mansour Hindawi, 31, in London, and Ahmed Nawaf Mansour Hasi, 36, in West Berlin. Hasi, who uses a different last name but is a full brother of Hindawi, has vehemently denied any role in the bombing of the La Belle discotheque in West Berlin April 5, in which an American soldier and a Turkish woman were killed and 230 wounded.

Allied intelligence sources have discovered that a top Syrian Air Force intelligence officer, Lt. Col. Haitam Saeed, repeatedly passed through West Berlin earlier this year. Some U.S. and Western European antiterrorist experts believe he personally supervised the bombing of the friendship club.

Hasi has told West German investigators that the explosive used in the friendship society bombing came from the Syrian Embassy in East Berlin. Saeed is believed to have played a key role in making sure the attack on the friendship society, twice botched earlier, would be a success on March 29, according to Allied intelligence sources.

The possible involvement of Saeed, the number two man in Syrian Air Force intelligence, is of particular interest to western antiterrorist experts because his boss, Mohammed Khouli, is extremely close to Assad and has served as Air Force intelligence director since Assad, a former Air Force chief, seized power in 1970. The Air Force intelligence unit has remained the small, elite body of Syria's complex web of intelligence services ever since.

The assumption of western intelligence services is that Saeed could not be involved without the knowledge and express approval of Khouli, and that Khouli, in turn, would not act without clearing any risky operations with Assad.

No evidence has yet emerged linking Saeed, or any other Syrian intelligence operative, to the La Belle discotheque bombing, however. West Berlin police chief Manfred Ganschow has said there are "still very, very few clues" linking the three men involved in the friendship society bombing to that at the discotheque.

The bombing of the friendship society's building was in keeping with the already established and well-known pattern of the Syrian use of terrorism to deal with its Arab enemies abroad. Direct Syrian involvement in either the La Belle discotheque or El Al bombings, with Israeli and American civilians as targets, would represent a new trend far more disturbing to western governments.

Sophisticated Technology

One confusing element for Allied investigators searching for the Syrian connection has been the sophisticated technology used in the El Al bombing plot. The plastic explosive -- which could not be spotted by regular metal detectors or X-ray devices -- was hidden in the bottom lining of a piece of hand luggage and the detonator concealed in a hand calculator.

Similar technology was used in another attempt to blow up an El Al airliner in December 1983 and a variation of it was use in the bombing April 2 of a TWA plane over Greece in which four Americans were killed. As in the latest El Al bombing attempt, the one in 1983 involved a woman who did not realize she was carrying an explosive in her suitcase. The suitcase went through airport security checks in both Athens and Tel Aviv, but the bomb failed to explode. It was finally discovered by British security in London.

The use of this kind of technology has been most closely associated with the May 15 Organization headed by Abu Ibrahim, known as the "master suitcase bomber." It is unclear where his base of operations is today.

French intelligence officials, working on the basis of confessions obtained from a recently apprehended Tunisian terrorist, Habib Maamar, say Abu Ibrahim is working out of Baghdad, but some U.S. antiterrorist experts believe he moved to Libya after Washington pressured the Iraqi government.

Experts familiar with the murky world of Middle East terrorism, where operatives often have ties with multiple Arab intelligence services at the same time, do not exclude the possibility that Hindawi could have been working on behalf of Abu Ibrahim. So far as is known, however, those terrorists arrested in London and West Germany have spoken only of Syria's backing for their operations and have not mentioned Abu Ibrahim.

Within the Reagan administration, CIA Director William J. Casey has taken a particularly hard line in public against Syria. In a speech here May 15 to the American Jewish Committee, Casey openly castigated Syria, together with Iran and Libya, for using its embassies, diplomatic pouches, communications channels and territory to aid various terrorist groups in their operations.

On the other hand, White House and State Department spokesmen have been far more reluctant to blame Assad publicly. This, they say, is because many "hard facts" are still missing and because the Syrian leader is regarded as too important a player in Middle East politics and in efforts for the release of Americans kidnaped in Beirut to dismiss as a wild-eyed terrorist fanatic. The prevailing administration line has been to await the results of British and West German investigations before reaching any final judgment.

The British, West German, French and Italian governments have all taken the same public diplomatic stance. But together with the United States, they have been pressing hard on Assad in private to crack down on the activities of known terrorist groups.

One administration official said Assad has passed word to the United States that he will curtail the operations of the Abu Nidal group and has expelled one or more of its members from Syria recently. Abu Nidal's Fatah-Revolutionary Command asserted responsibility for the attacks at the Rome and Vienna airports Dec. 27 that killed nearly a score of passengers and wounded more than 100. There are also reports that Assad is on the verge of a showdown with Iranian-backed Islamic fundamentalist groups in Lebanon who hold a dozen French and American hostages.

Intelligence officials of four Western European governments, Israel and the United States do not question Assad's deliberate and finely honed use of terrorism as an instrument of Syrian foreign policy to get his way in Lebanon, the Arab world and elsewhere.

Assad's Syria is generally held responsible, directly or indirectly, for the assassinations of Lebanese Druze leader Kamal Jumblatt in 1977 and Lebanese president-elect Bashir Gemayel in 1982 and for abetting Shiites who blew up the U.S. Marine barracks in Beirut in October 1983, killing 241 soldiers.

But most officials continue to doubt that Assad himself played a direct role in ordering the bombing of La Belle discotheque or that he approved, or knew beforehand, of Hindawi's decision to attempt to bomb the El Al plane, which carried 340 passengers, including more than 200 Americans.

The main reason for these doubts is both Assad's cautious character when it comes to matters of war and peace with Israel and the potential for a violent Israeli retaliation against Syria had the El Al airliner blown up. Assad is not believed ready to risk provoking a war with Israel at this time.

The El Al bombing attempt was a "mishap," according to a senior Israeli military official. "Someone took Assad's general guidelines, which are 'we have to do something,' and went too far."

The official was referring to Assad's presumed desire to retaliate in some fashion for the Israeli interception over the Mediterranean Feb. 4 of a Libyan executive jet carrying a top Syrian party offical. The Israelis mistakenly thought Palestinian terrorists were aboard.

"It's not like Assad, or for that matter Syrian intelligence, to conduct an operation without adequate deniability," the Israeli said.

The theory of a "rogue" Syrian intelligence officer possibly acting on his own is shared by many other western intelligence and government officials. It has already been dubbed by some Middle East specialists as the "Thomas a Becket Syndrome." Becket was the archbishop of Canterbury murdered at the vague suggestion of Henry II ("Will no one revenge me of the injuries I have sustained from one turbulent priest?").

The view of Syrian intelligence acting on its own implies that Syria today is ruled by a physically and politically weakened Assad, whose state of health has been a subject of continual speculation since he suffered a heart attack in late 1983.

Complex Network

During his 16 years in power, Assad has built up an enormously complex intelligence network, with several secret services and agencies -- estimated to number anywhere from five to nine -- working with a score of known terrorist groups. The question now is whether the Syrian leader's once tight grip on their day-to-day activities has loosened.

"It was inevitable that this network would get out of hand and turn some of its activities elsewhere," the senior Israeli military source said.

An analysis circulating in U.S. and Western European intelligence circles, however, asserts that Assad's control over his highly centralized intelligence network system has not slackened. Those holding this view note that various Syrian intelligence services have long been actively involved in providing logistical support, explosives and various forms of indirect assistance to Middle East terrorists active in Western Europe.

Middle East experts note three types of distinctly different relationships between Syria's secret services and terrorist groups and three different Syrian methods of using "cutouts," or agents whose actions cannot easily be traced to Damascus.

One method has been the creation of Palestinian factions such as Saiqa, which are virtually an integrated part of the Syrian Army and intelligence system and direct agents of the Syrians. Another is collaboration with, and logistical support for, radical Palestinian and Lebanese groups that remain largely their own masters and decision-makers but are often sent on terrorist operations by Syrian intelligence.

According to Iraqi and Lebanese sources, Syrian intelligence agents usually work with these groups by setting down guidelines on the kinds of targets to be attacked and selecting which countries they should operate in and which are to remain off-limits. But the choice of specific targets most often is left up to the groups themselves, these sources say.

Best Known Group

The best known of such groups in the West today is Abu Nidal's, which has taken responsibility for a number of attacks on Israeli targets in Western Europe and on Palestinians associated with his number one Arab enemy, Palestine Liberation Organization Chairman Yasser Arafat.

Abu Nidal's terrorist organization, which is small (200 to 300 members) but highly professional, is perhaps most famous for its nearly successful assassination attempt on the Israeli ambassador in London, Shlomo Argov, in June 1982 that served as the pretext for the start of the Israeli invasion of Lebanon.

To this day, it has never been clear whether Abu Nidal himself selected Argov as a target or was acting for the Iraqi government, his host at the time. Iraq has since broken all ties to Abu Nidal's group and expelled him from Baghdad. Both Iraq and Abu Nidal spokesmen in Damascus maintain that the decision to try to kill Argov was made by Abu Nidal on his own.

Abu Nidal, whose real name is Sabri Banna, now operates out of both Damascus and Tripoli, Libya. He is allowed by the Syrians to run an office in the Syrian capital and to train terrorists in camps located in the Syrian-controlled part of Lebanon's Bekaa Valley.

Assad said in a recent interview with The Washington Post that he has never met Abu Nidal but that he would continue allowing him to run "a cultural and political" office in Damascus and that he could not close his camp in the Bekaa.

The third and most complicated "cutout" system used by the Syrians is the selection of lone terrorists, "freelancers" or "sleepers," to accomplish a specific action. The convicted Lebanese assassin of president-elect Bashir Gemayel was such a case. Hindawi and Hasi also appear to fit into this category.

So far as is known to date, neither belonged to any well established Palestinian or Lebanese political group, though Hindawi is reported to have been a member of the Jordanian branch of the Syrian-backed, pan-Arab Baath Party. Hindawi was a freelance journalist in London and Jordan who was regarded as unstable by many of his closest friends and past employers.

An Unstable Relationship

Typical of his instability was his relationship to the Irish woman, Anne Marion Murphy, whom he tried to use to smuggle a bomb hidden in the bottom of a piece of her luggage onto the El Al flight. After a stormy six-year marriage to a Polish wife, Barbara, Hindawi broke up with her and began dating Murphy, a hotel chambermaid, in the spring of 1985.

According to British police sources, Hindawi's relationship with Murphy, like the one with his Polish wife, was "not very stable," with the Jordanian coming and going away, sometimes for weeks. Hindawi left Murphy -- pregnant, as it turned out -- about six months ago and only returned and offered to marry her about one week before the El Al incident.

The timing suggests that Hindawi had not originally intended to use Murphy as a bomb carrier and only came up with the idea a short time before the El Al bombing attempt. It also suggests his plot was hatched before the U.S. bombed Libya April 15 and thus not originally meant as retaliation for it.

Just whose idea it was to place a bomb aboard the El Al plane is far from clear.

The Pentagon source familiar with the British interrogation of Hindawi said the Jordanian and his brother had "offered" their services to Syrian intelligence months ago and were recruited and trained in Syria before returning to England and Germany to be left as "sleepers."

Subsequently, the brothers were "activated" by Syrian intelligence in East Berlin to carry out the bombing of the friendship society. But that act involved an intra-Arab squabble in which Syrian use of terrorist means is regarded as typical. However, Syrian involvement in bombing La Belle discotheque or attempting to blow up the El Al plane would be highly atypical.

Syrian aid for Hindawi in London apparently was considerable and included giving him a false Syrian passport to enter Britain and a letter from the Syrian Foreign Ministry in Damascus to obtain a visa. Hindawi also has said that he used a Syrian safe house in London and had extensive contacts with Syrian Embassy officials before and after the El Al incident.

These allegations were enough to convince British authorities of the need to interrogate three Syrian diplomats. When they refused to waive diplomatic immunity and would agree to questioning only within the Syrian Embassy, the British government expelled all three.

Unlike the British police, who have consistently given more credence to Hindawi's claims of Syrian involvement in the El Al incident, the British Foreign Office has been more doubtful. While Hindawi certainly had ties to Syria, Foreign Office officials remain skeptical the Syrian government helped to plan the operation or ordered it done because of the potentially far-reaching repercussions for Assad.

According to one Reagan administration source, Assad has admitted to Jordan's King Hussein that Syrian intelligence had contacts with Hindawi but regarded him as too unstable and unreliable to deal with. The Syrian leader told Hussein that when Hindawi came to the Syrian Embassy in London after his failed bombing attempt, officials there refused to take him in, the source said.

Even if Syria was involved, Foreign Office officials are doubtful the proof will ever be found. Unlike the Libyans, one official noted, "the Syrians are very careful to observe the proprieties. They have some concern for their international image."

That the "Syrian connection" to terrorism is extremely difficult to pin down was demonstrated last week in Italy. Italian judicial authorities issued arrest warrants for 14 Arabs implicated in a series of terrorist incidents last year. Abu Nidal was among the 14, but no Syrian official was named.

Italian officials said this was because no evidence had been discovered linking Syria directly to any of the incidents.