Sharp differences over the Iranian-Iraqi war threatened tonight to scuttle an Arab summit conference called to coordinate the struggle against Israel.

A special steering committee of Arab foreign ministers trying to perpare the ground for a full-scale meeting broke down in confusion as Syria vowed to boycott this summit, and all those in the future, unless the conference is postponed or has the Persian Gulf conflict as the first item on its agenda.

The firm Syrian position frustrated efforts by such moderates as Saudi Arabia and Jordan to gloss over intra-Arab differences for the sake of a united position against Israel, illustrating once again the Arab world's perennial difficulties in working togehter gainst its common foe.

Syria, a longtime political rival of Iraq, has openly supported Iran in the war, as have its radical allies, Libya and South Yemen. Jordan, the host for the summit, as well as Saudi Arabia and the gulf oil sheikdoms, have quietly backed Iraq.

Even more than he fears the possible loss of substantial Saudi aid, President Hafez Assad of Syria is understood to fear an Arab summit in which his principal rival, Iraq's President Saddam Hussein, would emerge as the strongest regional spokesman.

The summit, the Arabs' 11th such gathering of kings, ruling sheiks and presidents, had been expected to project a semblance of unity within the Arab world, which is divided by internal disputes, border conflicts, policy differences and personal political rivalry.

Arab moderates grouped around the newly formed axis of Iraq, Saudi Arabia and Jordan had hoped to concentrate on formulating a long-term strategy for dealing with Israel and continuing Arab opposition to the Camp david accords as well as dealing with the question of Arab economic cooperation. By doing so they had hoped that the disruptive issues of inter-Arab political discord could be passed over, at least for the duration of the conference.

That, however, is a concept that Syria, increasingly isolated among its fellow Arabs and hurting from an internal political crisis, has so far refused to accept.

A week ago, Syria asked that the conference, scheduled since the last Arab summit in Tunis a year ago, be postponed because of severe disputes among its members, which Assad has insisted should be resolved first. Libya, which announced a merger with Syria only two months ago, has supported that line, as has the Palestine Liberation Organization.

Assad's hard-line position was reiterated forcefully today by Foreign Minister Abdul Halim Khaddam in the seven-man steering committee. The group has been meeting here since last night to try to work out recommendations for a summit agenda to pass on to a gathering of all Arab foreign ministers, who are scheduled to meet here beginning Thursday.

According to Arab sources close to the participants in the committee meetings, they were "very hot." Khaddam argued against his fellow foreign ministers from Kuwait, Jordan, Saudi Arabia, Iraq, Algeria and the head of the PLO's political department, Farouk Kaddoumi, the sources said.

"If this summit does take place despite our objections," one Arab official quoted Khaddam as stating at one point, "then it will be the last summit held and it will mean the end of the Arab League."

Those were strong words, tinged with a sort of hyperbole that is common in Arab gatherings. But they did imply a serious threat to the summit.

The summit could go on without Syrian or Libyan and South Yemeni participation. But their boycott, if it did materialize, would detract from the summit's overall importance and only underline the very differences among fellow Arabs that its organizers had hoped to paper over.

Late tonight, after the preparatory committee's fourth turbulent session broke up, Khaddam left the hotel where the delegates were quartered with two PLO representatives, Kaddoumi and Yasser Abd Rabbo -- presumably to return to Damascus for urgent consultations with Assad.

As he was getting into Khaddam's limousine, Abd Rabbo confirmed the worst. "Until now," he said, "the position is that Syria will not attend the summit." The PLO representative hinted that it would follow Syria's lead. s

Khaddam would only state that "we have not yet agreed to an agenda --" words that left plenty of room for reopening negotiations, reconsidering positions and even seeking compromises.

Since calling for postponement of the summit, Assad has been under heavy pressure from the moderate Arab oil nations who subsidize his economy. They have insisted that he should back down for the sake of presenting to the world a solid Arab front, at least in the face of Camp David and Israel.

Only two days ago, the Saudi foreign minister, Prince Saud Faisal, flew to Damascus to try to persuade Assad to drop his opposition. Although the discussions were secret, Arab diplomats here in Amman believe that Saudi Arabia suggested that if Syria did not attend the summit, Saudia Arabia would reconsider its $1 billion-plus annual subsidy.