Like the tip of an iceberg, this week's reconciliation of Jordan and Egypt is part of deeper - not always visible - Arab political changes that may tempt the United States back into the Middle East peacemaking business.
But there have been parallel reminders of how great remain the obstacles to peace on both sides of the Arab-Israeli divide.
There have also been signs that the internal political clocks of the Arabs and the Israelis are dauntingly out of sync on the center-most issue of the Mideast conflict: the future of the Palestinians, notably the 1.2 million Palestinians in the West Bank and Gaza Strip which Israel captured in the 1967 war.
It is the Jordan-Egypt reconciliation - a move in which Jordan's traditionally cautious King Hussein ostentatiously defied opposition from fellow Arab leaders - that gives some veteran Mideast watchers reason for hope. They now see better chances than in the past for drawing Jordan into some kind of negotiated resolution of the West Bank question.
Israel, however, is politically hobbled by a July election that produced a ''national unity'' Cabinet wildly divided on the West Bank issue. Ironically, chances for Israeli concessions seem far better with avowedly hard-line Syria over the Israeli military presence in Lebanon - something virtually all Israeli politicians want to end.
Another potential area for at least cosmetic easing of tension involves Israel's peaceful but frosty ties with Egypt. Two of Egypt's stated conditions for returning its long-absent ambassador to Israel are a pullout of Israeli troops from Lebanon and progress on resolving the problem of Taba, a tiny slice of Sinai which Israel kept despite its 1979 peace treaty with Cairo. Israeli politicians think progress is conceivable on both fronts.
King Hussein's restoration of formal ties with Egypt, meanwhile, is less important in itself than for its timing and method. Despairing of making progress toward ''Arab unity'' on this or any other issue at a scheduled (but repeatedly delayed) pan-Arab summit, the Jordanian monarch decided it was pointless to wait any longer.
A year or so ago, this go-it-alone approach would have seemed unthinkable. But much has changed in the Mideast since then:
1. The Saudis, whose oil billions have long helped bankroll not only Jordan but also other major Arab states like Syria, aren't what they used to be on the regional power map.
The world is agush with oil - prices have fallen dramatically. So, naturally, has the volume of Saudi Arabia's direct aid to countries like Jordan and Syria. At the same time, politically, Egypt's post-Sadat reintegration into regional politics in everything but name has put a brake on Saudi Arabia's gradual inflation to the status of Arab superpower.
Full-scale Saudi opposition to King Hussein's move might have delayed the formal reconciliation with Egypt. But as it was, the Saudis seem to have told the King something like this: We don't like the idea of your breaking Arab ranks on the issue, but we're not going to make a federal case of it. And they didn't - limiting themselves to low-key criticism of the King's move.
2. The Palestinians' independent political clout, in the person of Palestine Liberation Organization chief Yasser Arafat, is also not what it used to be. Chased out of Lebanon, his guerrillas scattered far from Israeli frontiers, his PLO standing challenged by Syrian-backed rivals, Mr. Arafat isn't in a position to veto the King or any other Arab leader these days.
At least for the present, Arafat needs Arab leaders' political support more than they need his. This is especially true of Syria's two fellow ''front-line'' Arab states on Israel's border: the recent reconcilers, Jordan and Egypt.
3. Generally, an era of suicide truck bombers has prompted jitters among relatively pro-Western Arab regimes. Again, Jordan and Egypt are prime examples. The Saudis also belong on the list, deeply concerned as they are about the danger of political extremism within their own borders.
In Jordan's case, neighbor and rival Syria is seen as a less amorphous threat. But Jordan's evident reasoning was - reconciliation with Egypt or not - the Syrians and Jordanians are destined to be on tense, though probably not warlike, terms for some time to come. And at home, the Jordanians must meanwhile deal with a majority Palestinian population as aware as everyone else watching the Mideast these days of the bleak chances for visible negotiating progress on the West Bank.
The result of all these factors was the high profile rapprochement with Egypt. Immediately afterward, Mr. Arafat was brought on stage for talks in Amman. Then Egyptian President Hosni Mubarak himself showed up for a summit with King Hussein.
In the best of all possible Jordanian worlds, whoever wins the coming US presidential election will promptly seize on this new sign of Jordanian-Egyptian assertiveness to attempt a new West Bank peace initiative. After all, some Jordanians reason, Israel's faltering economy could facilitate a more muscular US drive for Israeli negotiating concessions on the West Bank issue; especially if President Reagan gets reelected and becomes America's only full second-term executive since Eisenhower.
Fundamentally, however, the Jordanians, Egyptians, and just about everyone else in the Mideast seem to reckon that Israel's internal political deadlock makes West Bank negotiating progress unlikely.
Said one conservative representative of the Israeli government: ''All it will take to topple this Cabinet is a serious new US initiative'' on the West Bank.
And it remains unclear whether King Hussein's go-it-alone approach on Egypt implies a change in his fundamental unwillingness in the past to brook any West Bank negotiating approach failing to ''guarantee'' from the outset that Israel will hand back virtually the entire area.