King Hussein of Jordan formally opened a divisive Arab summit today amid last-ditch mediation to coax an important bloc of boycotting hard-liners to join the session in a final face-saving gesture of Arab unity.

The king's calls for Arab solidarity and a united strategy for defending Palestinian rights rang loftily in the domed auditorium of Amman's new Royal Cultural Center before the 15 rulers and prime ministers who gathered here. But they seemed hollow in view of the fact that six of the stuffed chairs at the summit's U-shaped conference table -- including that of the Palestine Liberation Organization -- were empty, underlining the disunity that has all but doomed the conference.

The absence of the Steadfastness Front -- Syria, Algeria, Libya, South Yemen and the PLO, joined this time by Lebanon -- made any real discussion of the planned united Arab political strategy for confronting Israel all but meaningless. As a result, today's conference limited itself to two brief sessions. Then it adjourned for 24 hours to allow Arab leaders to mount one last mediation effort to convince the boycotters to come to the conference.

In all, the 15 leaders of the 21-nation Arab League that met here talked for only a little over three hours -- two of which were given over to routine opening speechmaking by the conference host, Hussein, and the secretary general of the sponsoring Arab League, Chadli Klibi.

After an afternoon of bilateral private exchanges among the various heads of state and prime ministers here at their heavily hotel quarters on the outskirts of the city, it was decided that the key discussion of a joint Arab political strategy for the future -- the first item on the agenda -- should be postponed pending the mediation efforts.

Instead of dealing with the political issues this evening, the summit met behind closed doors for just a little over one hour and passed a series of uncontroversial proposals for future economic planning, investment and development in the Arab world.

When the meeting ended, conference spokesmen announced that there would not be another meeting until 6 p.m. Wednesday, which would allow Arab leaders here to make one last appeal to the boycotters, led by Syrian President Hafez Assad.

Conference sources did not exclude a lightning visit to Damascus by a committee of heads of state here to try to work out an accord with Assad.

In an apparent attempt to demonstrate its displeasure with the decision to go ahead with the summit in Amman, Syria has moved at least a brigade of troops, more than 8,000 men and perhaps 200 tanks, close to its border with Jordan in the last several days, according to Washington sources.

[A U.S. official familiar with the intelligence on the Syrian maneuver called it a "crude and heavy-handed move" that is "bizarre" even by Middle Eastern standards. There was little belief in Washington or Amman, according to the official, that the Syrian show of force was the prelude to actual military action.]

While officially the surprise 24-hour intermission in the summit was being portrayed as just a routine period for further small private meetings among the Arab leaders here, Arab sources said that one compromise that was being discussed was the proposal to limit the Amman summit to the economic issues that had already been approved by the boycotters in a preparatory meeting of Arab foreign ministers last week.

These sources said under the terms of this proposal, summit leaders here might be prepared to guarantee the boycotters that the controversial political issues would be postponed until a later conference next year after a conference of Islamic leaders to be held in Saudi Arabia in January.

Assad repeatedly demanded that the Amman summit, scheduled at the last Arab summit in Tunisia a year ago, be postponed because of the intense divisions between Arab states -- a result of the sharp cleavage in the Arab world over Iraq's war with Iran.

The two-month-old gulf war has forged a powerful moderate-to-conservative alliance among Iraq's President Saddam Hussein, King Hussein of Jordan, King Khalid of Saudi Arabia backed by the rich gulf sheikdoms.

This bloc has dominated the opening sessions of the conference here, just as Assad feared they would, forcing his militant Steadfastness Front into a minority position.

At the foreign ministers' meeting last week, Assad tried to stave off the present summit by proposing a series of small "minisummits" to thrash out the divisions among Arab nations prior to a full summit meeting. The Iraq-Jordan-Saudi Arabia bloc, however, refused to have anything to do with the proposal, insisting that the summit meeting should go on as planned.

When the summit could not be postponed, Syria announced that it would boycott it.

Syria and its allies have been greatly embarrassed by the gulf war, which has built up the political importance of Saddam Hussein, long one of Assad's leading critics and rivals in the Arab world. As a result Assad and his allies have supported Iran.