Jerusalem — A series of signals from several Arab capitals indicate there may be unprecedented openings for progress on Israeli-Arab peace over the next few months:
* Both United States and Israeli experts believe Jordan's King Hussein is likely at least to announce readiness to join peace negotations, under certain conditions, in the next couple of months.
* Iraq, whose acceptance of such a Jordanian position would be a key support for the king, this week released the text of a conversation between Iraqi President Saddam Hussein and a US congressman in which the Iraqi leader was quoted as accepting - apparently for the first time - Israel's need for security.
* The mainstream of the Palestine Liberation Organization is expected to give at least a tacit green light to negotiations by King Hussein and approved Palestinians (who are not official PLO members) with Israel over a solution to the Palestinian problem.
At the same time, however, two other developments underline the obstacles facing prospects for achievement of a wider Middle East peace: the initial sluggish pace of Israeli-Lebanese talks over withdrawal of Israeli troops from Lebanon and future Israeli-Lebanese relations, as well as a postwar military buildup by Syria.
Dr. William Quandt, top Middle East expert on the US National Security Council under the Carter administration and currently with the Brookings Institution in Washington, D.C., told several Israeli groups upon his arrival from Amman this week that Jordan will probably announce ''within the next month or two'' that it is ready to join the peace process.
The catch: Jordan would demand US assurances of a freeze on building of Israeli-Jewish settlements on the West Bank and in Gaza - home to 1.3 million Palestinians and the land for which Jordan and the Palestinians would bargain in order to set up a Palestinian homeland linked to Jordan. Israel, which seized such settlements as a guarantee that the West Bank will not return to Arab sovereignty, has refused a freeze and stepped up the pace of settlement building.
But Mr. Quandt expected that Jordanian willingness to negotiate would be publicly announced under the present circumstance, but with the rider that a freeze would have to come into effect once negotiations began. He believes the US would back Jordan on a freeze during negotiations.
Foreign Minister Yitzhak Shamir said Wednesday, ''We read in the press that King Hussein is seeking an Arab mandate to join neogitations. Such an Arab mandate would be so extreme as to be rejected by all Israelis.'' The foreign minister rejected any Israeli return to pre-1967 borders, a demand made by Jordan and other moderate Arab states.
Mr. Quandt said there was an expectation in Amman that ongoing PLO-Jordanian consultations would produce ''tacit if not explicit agreement to the Jordanian-Palestinian initiative which is coming.'' A similar scenario was predicted to the Monitor by well-informed Palestinian sources in Beirut who said a dramatic PLO peace initiative was not likely. PLO chairman Yasser Arafat has indicated, in a recent interview with the Egyptian weekly al-Mussawar, that he might be prepared for mutual recognition with Israel.
PLO acquiescence to a Jordanian negotiating role is critical since a 1974 decision by the Arab League - a decision now eroded but still symbolically potent - gave the PLO sole responsibility to represent the Palestinians. With PLO concurrence, the king could count on backing from Egypt and probable lack of opposition from Saudi Arabia and Iraq.
But the slow pace of talks between Israel and Lebanon, in which the US is playing a key role, puts a crimp in this scenario. Jordan had indicated that progress on withdrawal of foreign, notably Israeli, troops from Lebanon will be a key test of US sincerity and reliability. The US is pushing for speed - it reportedly told Jordan that troop pull backs will begin in about two months time.
But the talks are now bogged down over Israel's demand to place ''normalization'' of relations high on the agenda and Lebanon's insistance that the talks focus primarily on Israeli troop withdrawal and security arrangements. Israel has no reason to hurry just to assist US plans for the future of the West Bank and Gaza, on which Israel and the US are at odds.
Syria may also prove a stumbling block. The Syrians are annoyed at the prospects of Jordan joining peace talks and at the possibility of Lebanese concessions to Israel.
In a highly unusual announcement the Israeli military spokesman yesterday revealed that Israel has information that the Syrians are building two new bases for Soviet-made long range SAM-5 ground-to-air missiles deep inside Syrian territory.
The missiles by themselves do not appear to provide a new military threat. But their deployment - for the first time outside the Soviet Union - could hint that Syria, perhaps with Soviet encouragement, will drive a hard bargain on withdrawal of its troops from Lebanon. If Syria stays in Lebanon so will Israel and if Israel stays, any Jordanian peace initiative will collapse.