For us longtime true believers, the admission does not come easily, but come it must after an on-the-spot inspection trip to the Middle East: only the unfinished business of the Israeli-Egyptian peace treaty, scheduled for completion by April 25, is keeping the Camp David "peace process" alive.

It may linger on after the final withdrawal of Israeli forces from the last piece of occupied Egyptian territory on the Sinai. But the rest of the process-- having to do with self-rule for the Palestinians on the West Bank and the Gaza strip--is going to become harder and harder to hold within the relatively manageable confines of the Camp David framework for peace.

As a consequence, it is likely to become a lot less susceptible to U.S. influence. For as long as there is no solid alternative at hand, the temptation will be strong for just about anybody and everybody--the so-called moderate and the so-called radical Arabs, the Europeans, the Soviets--to work their way into the act.

The upshot could be chaotic, ending in a dangerous polarization: Arabs, plus Europeans, plus Soviets loosely lined up against an isolated Israel in support of some variation on the Saudi Arabians' "Fahd plan." Or it could, conceivably, be constructive, which bring us to this week's White House visitor, Egyptian President Hosni Mabarak, the cautious, workmanlike, distinctly uncharismatic and strikingly dissimilar successor to Anwar Sadat.

The dissimilarities pretty much ensure that what we hear from him publicly will be reassurances of continuity: a perfunctory re-plighting of Egypt's troth to Camp David. Good form demands no less, and from Mubarak's standpoint, so does good sense. The urgent personal involvement of Secretary of State Alexander Haig in a search for life-signs in the Camp David "autonomy" talks is an insurance policy of sorts against anything Israel might do that could threaten orderly completion of the peace treaty and the recovery of Egypt's territory.

But what Ronald Reagan will hear from him privately may be something else again, depending on how much of what Mubarak's advisers are saying in private will actually be conveyed explicitly at this first encounter between the two presidents.

Paraphrased, what Mubarak's men say is that prospects for anything more than a vague Egyptian-Israeli rededication to the "autonomy" principles before April 25 are next to nil. They see the Israelis as adamant on the one autonomy issue on which Egypt cannot afford, for the sake of its relations with the Arab world, to yield: the right to vote in any West Bank self-rule arrangement for some 100,000 Palestinians in East Jerusalem. Israel has formally annexed East Jerusalem as part of its capital.

Only U.S. "leverage," they insist, can force Israel to reverse its efforts to consolidate its presence on the West Bank in ways that effectively foreclose "full autonomy" for its Arab inhabitants. A "disaster" is the way one official describes Israel's occupation policy.

What is more, officials in Cairo say they see "no evidence" that Reagan understands. "It is going to be up to us and the Europeans," says one, "to convince the United States to use its influence on Israel."

As an inducement, Mubarak's people offer the prospect of Egyptian honest brokerage. In pursuit of Arab "moderation," Egypt would present itself to the Arabs as the only Arab nation in a position, by virtue of the peace treaty, to deal with Israel. To the Israelis, Egypt would present itself as Israel's only friend in the Arab court.

"If Israel would only give us concessions, we could help lead the Saudis and others into a more moderate stance," says one Egyptian policy-maker. "Why wouldn't Israel want to help its new Arab partner do things that in the end would help Israel?" he asks.

It's a nice idea, flawed only by the extraordinary demands it would put not only on Israel but on the United States. If the Camp David formula is already unacceptable to Prime Minister Menachem Begin's government, how could a compromise between it and the much more extreme and (for Israel) unpalatable "Fahd plan" be made more acceptable?

At this point the conversation returns to the need for U.S. "leverage."

The new Egyptian leadership, then, is characterized by a striving for the best of many worlds, including: a small, slow opening to the Soviets which will probably lead to resumption of full diplomatic relations; continued heavy reliance on American economic and military aid, but not total dependence (note the recent purchase of French jet fighters); a return to prominence in the leadership of the Arab world; a reknitting of connections with the "nonaligned"; a diminished enthusiasm for "strategic consensus" or the sort of American military presence in Egypt that Sadat was encouraging.

It adds up to a slow but sure change in Egyptian orientation, with profound, if not clearly predictable, implications for the old order of the Camp David accords.