US keeps up momentum in Middle East

US diplomacy is not standing still in the Middle East, despite the temporary breathing space offered by the Arab hard-liners' torpedoing of the Saudi peace plan for the region.

US Secretary of Defense Caspar W. Weinberger was in Morocco Dec. 3 for talks with officials. Their main topic: the possibility of increased United States aid for Morocco to counter the Soviet weaponry reportedly reaching the Polisario guerrillas challenging Moroccan authority in the Western Sahara.

From Morocco, Mr. Weinberger flies to Ankara to discuss increased US aid to Turkey and its role in overall security arrangements in the arc from the Bosporus through the Gulf, to the Himalayas.

Already at the eastern end of the Arab world is US special envoy Philip C. Habib. Since last weekend he has had talks in Lebanon and Syria, was in Jordan Dec. 3, and was expected next in Saudi Arabia before heading for Israel.

The Habib mission is intended largely to reassure Israel. US-Israeli relations have been severely strained since the summer because of what Israel sees as the Reagan administration's tilt toward Saudi Arabia - and away from Israel.

Mr. Habib's official aim is to allay Israeli concern about the continued presence of Syrian surface-to-air missiles in Lebanon and about alleged Palestinian violations of the cease-fire in southern Lebanon negotiated by Mr. Habib in July.

This week has already seen two other US moves to reassure Israel:

* Negotiation of a formula acceptable to Israel for eventual European participation in a Sinai peacekeeping force.

* Signature of a US-Israeli agreement on strategic cooperation between the two countries.

Both moves have provoked protest from the Arab world, above all from the hard-liners. While Mr. Habib was conferring with Syrian President Hafez Assad in Damascus Dec. 2, a massive anti-Israel and anti-US demonstration was taking place in the Syrian capital.

But a case can be made that the US-Israel agreements are as much cosmetic as substance, as some critics of them in Israel suspect. The critics, however, failed in their efforts to defeat the Begin government in a vote of confidence in the Israeli parliament Dec. 2.

The overall immediate aim of the Reagan administration seems to be to head off any precipitate action by Israel that might provoke a crisis in the area.

Ironically, the Arab hard-liners at the Fez summit last week achieved in a few hours what Israel had failed to do in weeks of tireless effort. That was to remove from the immediate diplomatic agenda the Saudi peace plan that the Begin government had found so threatening - particularly after the Reagan administration had reacted positively to part of it.

What happened in Fez must have relieved the Israelis for the moment. It was a victory for them and a humiliating defeat for the Saudis and other Arab ''moderates.'' But Israelis must already be wondering whether the US, counting so much on Saudi Arabia in its strategic planning for the Gulf, may not be considering how to help the Saudis recoup what was lost at Fez.

Will Mr. Habib, for example, raise that very question when he is in Saudi Arabia later this week?

While there, will he also explore with his hosts the present stalemate in the Gulf war between Iraq and Iran in which both sides have reported an upsurge of fighting in recent days?

Iraq was one of the hard-liners who helped torpedo the Saudi plan at Fez. To some extent, this was a reversal of the rapprochement between the two countries signaled by Saddam Hussein's visit to Saudi Arabia in August 1980. The Gulf war had strengthened the rapprochement, since both Mr. Saddam and the Saudi royal family saw Ayatollah Khomeini's Shia Muslim fundamentalism in Iran as a threat to themselves.

What made Mr. Saddam join in the humiliation of the Saudis at Fez?

Has his failure to score a quick victory over Iran at last produced a measure of domestic opposition that he cannot ignore? More particularly, is there a factual basis for reports from Europe that dissident Iraqi Kurds, Iraqi Shia Muslims, and Iraqi Baathists are trying to develop some common action against him?