THE SPARE official briefings from the first two days of the Blair House sequel to the Camp David summit make it all sound almost too easy. "A good beginning" has been made; the atmosphere is "cordial, friendly and constructive." Secretary of State Cyrus Vance is predicting an agreement on a peace treaty between Egypt and Israel by the first anniversary of Anwar Sadat's ground-breaking visit to Jerusalem - "if everybody works fast."

It looks, in other words, almost too good to be ture. And so, predictably, warnings are already being sounded in some quarters that it is too good to be true. The skeptics are concerned that quick success in building in that part of the Camp David "framework for peace" that has to do with an Israeli-Egyptian peace treaty will actually spoil the prospects for completing that part that would settle the wider conflict over the West Bank and Gaza, resolve the grievances of the Palestinians, and lead to a comprehensive and enduring settlement. With Egypt neutralized militarily as far and away the most powerful champion of the Palestinian cause, the theory goes, the rest of the Arabs will pose no serious threat, and Israel will lose further interest in fulfilling the rest of the bargain.

Perhaps. But it has been our conviction (only occasionally shaken during some difficult passages earlier this year) that in their initial Jerusalem encounter, President Sadat and Israeli Prime Minister Menachem Begin set out, as we said at the time, "on a road on which there can be no turning back." And that is more than ever our conviction now.

This is not to dismiss out of hand the signs of potential trouble. Jordan's King Hussein, whose eventual participation is crucial, is playing a cautions waiting game. The Saudi Arabians, also crucial, are a lot more commital in private than in public. The Syrians are behaving like . . . Syrians. The Iraqis and Libyans and the other spoilers, who would wage war on Israel right down to the last Egyptian (or Syrian) soldier, ar predictably blowing hard. And so are the terrorists of the Palestine Liberation Organization, who make war on the innocent.

The Israelis, it has to be added, are not making life any easier for Mt. Sadat with his Arab brothers by their inflammatory emphasis on a "separate" peace with Egypt. And Mr. Sadat isn't making it easier for Mr. Begin with his Israeli constituents by emphasizing tight linkage between an Israeli-Egyptian peace treaty and a concurrent resolution of the whole Palestinian questions.

But the truth is that it is possible to find some reinforcement for both perceptions in the emential flexibility - the artful ambiguity, if you will - of the Camp David "framework" itself. And given the fundamental conflicts of interest that remain between Israel and its Arab neighbors, that is as it should be; as with an airplane wing or a suspension bridge or any delicate piece of construction subject to inevitable strems, a certain flex had to be built in.

Thus President Carter was not engaging in doubletalk but sensibly acknowledging the realities in his response the other day, when he was pressed at his news conference about the issue of "linkage". The two discussions, on the Sinai, which relates to Egypt and Israel only, on the one hand, and the West Bank-Gaza Strip discussions on the other, are not legally interconnected," he replied, "but I think throughout the Camp David talks and in the minds of myself, Prime Minister Begin and President Sadat, they are interrelated."

The problem, of course, will be to preserve the critical interrelationship - and in this Mr. Carter will have a vital part to play.But the commitments mutually exchanged at Camp David, and more or less explicitly expressed in the accords, will strengthen his hand. If a peace treaty with Egypt can be calculated to ease the pressure on Israel, it can also be calculated to alter Israel's own estimate of the risks it can then afford to take in coming to terms on the West Bank. Similarly, with Egypt at peace with Israel, the Arabs, hard-liners as well as soft-liners, would almost surely have to reassess their own capabilities and objectives. The cumulative effect over time, we believe, would be to transform fundamentally the atmosphere - and ultimately the terms - in which both sides could address and eventually resolve the hard, bedrock issues having to do with the rights and interests of Arabs and Israelis alike.

Nothing is certain about any of this, we suppose. But we remain more than ever encouraged in the belief expressed in this space almost a year ago that "the peace for which the Middle East has waited and suffered is coming to be." It will come slowly, incrementally, perhaps painfully. But it will come a lot closer in one huge Progression if the negotiators at Blair House move as easily and rapidly as they now appear to be moving toward a peace treaty between Egypt and Israel.