The United States ignored the eight-point Saudi peace plan when it first surfaced three months ago. Its timing, for one thing, was awkward; President Sadat was then on a visit to Washington. But President Reagan and his aides now are cautiously supporting the Saudi initiative as having potential for nudging along the peace process in the Middle East. It is not explicitly stated which parts of the plan are seen to be helpful and which are totally unacceptable. But the administration is prudent to be picking up this diplomatic ball and seeing what can be done with it.
Israel, not surprisingly, is opposed to Crown Prince Fahd's initiative, and a virulent Israeli campaign against it can be expected. Prime Minister Menachem Begin is right in declaring that it is not the basis for a political solution to the vexed problem of Palestinian self-determination. Many of the eight points - such as calling for Israeli evacuation of ''all'' Arab territories seized in the 1967 war and for setting up a Palestinian state with East Jerusalem as its capital - are patently nonstarters.
Yet the plan represents a significant step forward which ought not to be discarded out of hand. In the first place, the Saudis now have taken an initiative on their own, saying publicly what they have been saying privately all the time. In the past they have simply gone along with the Arab ''confrontation states,'' which have adamantly opposed the Camp David peace framework.
Secondly, the plan itself contains several elements which are not inconsistent with the Camp David formulas. Thus, one point affirms the ''right of all countries of the region to live in peace'' - an implicit recognition of Israel's right to exist. Another proposes a ''transitional period'' in the West Bank and Gaza under United Nations supervision, which is similar to the underlying concept of the Camp David autonomy agreement (which allows for a five-year period of transition). These elements would seem to offer room for negotiation.
No one believes that the Fahd plan is more than a starting point, or that it can at present supplant the Camp David negotiations. But there is no reason why it cannot be brought into the talks, as Henry Kissinger suggests, or why the United States should not encourage the Saudis and other moderate Arab states - notably Jordan, whose King is now in Washington - to become involved in a collective search for solutions. They and other Arab leaders were, after all, invited to join such a quest at the time the Camp David accords were signed. So giving a tentative US nod to the Saudi initiative is within the spirit of Camp David.
But the relevant point is that the Camp David autonomy talks, in process for two years now, do not look hopeful. They can succeed only if Israel radically changes its policies to bring them in line with US and Egyptian perceptions of what Camp David is all about. At the moment Israel is pursuing actions, such as settlement of the West Bank, which are an obstacle to reaching agreement. Hence if the talks end up stalemated, as many expect, it would be all to the good if the ground were being laid for other approaches.
The Saudi plan, however imperfect, offers something to work with. It helps broaden the negotiations by bringing in Israel's eastern neighbors. It also comes against the background of pressures on the newly elected President of Egypt, Hosni Mubarak, to edge back toward amicable relations with Saudi Arabia and the other Arab states. Taken together, some Mideast hands feel, these factors could coalesce in a clear-cut expression of willingness to make peace.
In sum, President Reagan may not win any cheers from Mr. Begin for warming to a Saudi role - and he will have to deal sensitively with Israel's growing, if exaggerated, anxieties over Washington's evolving posture of evenhandedness in the Middle East. But, in the interests of a comprehensive peace that will bless Israel as well as its neighbors, he is right to keep an open mind