An increasingly assertive bid by Jordan's King Hussein to foster a more moderate Arab power lineup may soon run up against twin hurdles thousands of miles away - on Capitol Hill in Washington.
And within the Arab world, potential roadblocks remain to the apparently intended diplomatic entente among Jordan and regional partners like Egypt, Iraq, Saudi Arabia, and Yasser Arafat's Palestine Liberation Organization.
In the days ahead, Congress is expected to weigh two important Mideast issues: the transfer of added United States military equipment to Amman to facilitate Jordanian support for less powerful or well-trained armies of nearby Gulf regimes; and the future of the US Marine contingent in Lebanon.
The Jordanians are hoping the Reagan administration will find a way around misgivings within Congress - and in Israel - over the $200 million package of military aid for Jordan.
As for the marines, the hope here is that a Democratic Party move to recommend their ''orderly'' pullout will not prod a premature withdrawal. The Jordanians - and Egyptians - share with many US politicians a sense that the Marines, and their European partners in Lebanon's multinational force, have become targets more than effective peacekeepers. But the concern here and in Cairo is that a hasty withdrawal at this stage might generally impair US credibility in the Mideast and boost regional extremists.
Recently the King's diplomacy has taken on increased momentum. Egypt Monday formally accepted an invitation to rejoin the Islamic Conference Organization after a five-year exile over its peace with Israel. And following last month's ICO invitation to Egypt, in which Jordan is understood to have played a role, Amman officials leaked reports that Egyptian President Hosni Mubarak would pay an official visit to Amman in February.
The Jordanians also let it be known Mr. Arafat would come here this month to resume talks, broken off last spring, on a joint Jordanian-PLO diplomatic strategy.
The leaked report of a planned Mubarak visit was especially significant. Such a trip, if made in February, would preempt a full Arab summit set for March 30 and thus represent a departure from King Hussein's traditional search for regional assent before major diplomatic moves.
Egypt remains formally suspended from the Arab League, although there has been ever closer contact in recent months between the Egyptians and both Jordan and war-strained Iraq. The Saudis, too, recently dispatched their first envoy to Cairo since Egypt's ouster from the Arab mainstream in 1979.
The Mubarak visit to Jordan is, according to the officially leaked report here, to be paired with a stop in Iraq.
But further hitches - or delays - in any reconciliation process are possible.
King Hussein's departure Wednesday on a health-related visit to the US will delay any meeting with Arafat or Mubarak until at least mid-February. Sources here say the King will travel to Cleveland for a medical checkup and probably return to Amman in two or three weeks. Informal talks with senior US officials are likely.
In the case of the Hussein-Arafat talks, Jordanian officials remain concerned that the PLO chief may prove either unable or unwilling to agree with Jordan on a joint diplomatic strategy aimed at a negotiated end to Israel's nearly 17-year occupation of the West Bank of the Jordan River and the Gaza Strip. The King seems to want agreement on a formula swapping Arab recognition of Israel's right to secure existence for Palestinian ''self-determination'' on the West Bank and in Gaza.
As for the Hussein-Mubarak meeting, at least one ranking official here speaks privately of ''pressure'' for the King to hold off on the encounter - presumably at least until after the Arab summit in Saudi Arabia. Apparently backtracking on the leaks of a planned Mubarak visit, officials here now suggest that although the visit is on the agenda, no firm date for it has been set.
Western diplomats suspect one key opponent to the idea of a Mubarak visit before the Riyadh summit may be Saudi Arabia. The Saudis have long sought to avoid alignment with any one camp in a divided Arab world - providing hefty aid to such countries as Jordan and Iraq, and to their major rival, Syria.
Sources close to King Hussein suggest he would be very reluctant to risk a split with the Saudis. Meanwhile, he is proposing that the Arab League abandon its tradition of unanimous decisionmaking in favor of majority rule. He hopes thus to finesse expected opposition from Syria and others at the Arab summit and win endorsement of a peace platform that, with US help, might pressure Israel to cede its tightening hold on the West Bank and Gaza.
Officials stress that the new lineup envisaged by the King would involve friendship - not alignment or alliance - with the US. Hussein hopes to avoid an irrevocable split between relative moderates in the region and rivals like Syria. Also, the Jordanians feel any workable negotiated settlement in the region must at some stage involve both the Syrians and the Soviet Union, which possess effective veto power in the Middle East.
Syria, with some 40,000 troops in Lebanon, could well further complicate the marines' position there. Moscow, in addition to being Syria's military supplier, holds a seat on the United Nations Security Council and could block any Western move to replace the multinational force with a UN contingent.