This is a week which could see a step-up of momentum toward a Middle East peace. If, that is, President Reagan can persuade visiting King Hussein of Jordan to join the talks on Palestinian autonomy.
One never likes to say that time is running out for a peace initiative. But it is clear that, the longer Jordan and the Palestine Liberation Organization now delay, the less there will be to negotiate about. This is so because Israel continues its policy of creeping colonization of the West Bank with relentless single-mindedness. The present population of about 25,000 Jewish West Bank settlers will be doubled in the next three months as 6,000 new housing units come on the market. All told, Israel is now estimated to own more than half of the land in the West Bank.
King Hussein must calculate the consequences of not agreeing to join talks based on Mr. Reagan's peace plan, which calls for Israeli withdrawal from the West Bank and establishment of some kind of a Palestinian entity there ''in association'' with Jordan. Time is of the essence. As the Jewish presence in the West Bank expands, the King could find his country having to cope with an influx of Palestinians fleeing Israeli rule. He is also mindful of Prime Minister Begin's insistence that the Palestinians already have a state of their own - Jordan. So the Jordanian monarch has good reason to negotiate.
He wants, of course, to march in step with the PLO, and the PLO is still far from accepting the Reagan peace formula. Yet PLO leader Yasser Arafat and King Hussein are gingerly moving closer together. After two days of meetings in Amman recently they spoke of a future ''special and distinguished relationship'' and hinted that they had agreed on a way to bridge the gap between the PLO position taken at the Fez summit - demand for an independent Palestinian state - and Mr. Reagan's plan. Among the understandings between them is that, once an independent Palestinian state was established, it would hold a referendum on joining a confederal ''association with Jordan.'' This is one aspect of a PLO compromise which King Hussein will present at the White House.
Meanwhile, other developments are also worth noting for what they may augur for a resumption of the peace process. One is that a new mood of pragmatism is reported in the West Bank itself, where concern grows that Israeli settlement policy will soon make an Israeli withdrawal moot. There appears to be heightened support for a mutual Israeli-PLO recognition, a PLO-Jordanian rapprochement, and PLO acceptance of UN resolutions 242 and 338 that provide the framework for peace negotiations. This is paralleled by a rising chorus of concern among the Jewish community abroad about Mr. Begin's annexationist policies.
And still another straw in the wind is the toughening stand in the White House, where President Reagan has pointedly let it be known that he is irritated with Israeli footdragging in Lebanon and West Bank settlement policy. One manifestation of this concern is a holding of the line on US aid for Israel. The administration failed to stop the Senate from providing more economic and military assistance than the President wanted for the next fiscal year, but it finally did manage to reduce the aid package. The signal to Israel seems clear.
However, if King Hussein and Mr. Arafat expect Washington to carry the diplomatic ball and exert the pressure that may be required to stop de facto Israeli annexation of the West Bank, they must be willing to sit down and negotiate. If they dally much longer, they will find Israel unilaterally settling the land - and the issue.