IT WAS NEVER possible that, on a single high-profiled visit, Zbigniew Brzezinski could sweep away all of Saudi Arabia's and Jordan's misgivings about an Egyptian-Israeli peace.It was predictable that they would wish to show themselves impervious to an American diplomatic blitz. And Saudi Arabia and Jordan are weak countries which necessarily conduct a policy of caution and indirection: It is not in them to give the United States a flat, quick yes or no.

This is not to say it was a tactical error to send a high official at this time to brief two governments whose cooperation is important to the second -- Palestinian -- stage of Camp David. But it is wrong to say that Mr. Brzezinski "failed." No one will know for months whether his mission, and the countless other consultations and messages that must be part of the selling of peace, help the process along.

In this task, President Carter seems to have accepted the common perception of Mr. Brzezinski as a strategist and Secretary of State Vance as a negotiator. Mr. Brzezinski, on his trip, apparently emphasized American sensitivity to the region's security concerns, meaning threats from radical Arabs and Russians. Mr. Vance, on television, came down hard on the theme that Camp David offers the only feasible route by which other Arabs can gain satisfaction for the Palestinians and the return of further territory. The Saudis in particular, even as they seek more American firmness, fret about American constancy.The Jordanians, though without an alternative to American diplomacy, fear reliance on it. But the United States has a couple of good cards in its hand.

What should be expected of the Saudis and Jordanians? The Saudis, of course, have not only peace but also oil on their mind. Whether their fragile internal balance allows them to be reasonably cooperative on either is not certain. Americans can hope, though, that on oil the Saudis will act on supply and price in a manner serving their own interest in a healthy world economy. On diplomacy, if they and the Jordanians cannot yet see their way to being helpful, they should refrain from being unhelpful, at least while the United States strives to prove it is serious about pressing the Palestinian component of Camp David.

During this period it would be a great mistake for Washington to get "tough," as some Americans seem ready to do. However insecure they may feel, the Saudi and Jordanian royal families are old and, in their way, valuable friends. They are entitled to ask how American policy serves their ends. The United States owes them a patient and honest answer.