Well within the traditional first 100 days, and pretty much on schedule if the Kennedy timetable is taken as a precedent, the Reagan administration is having its first foreign policy fiasco.

You might call it the Bay of AWACS.

The off-again-on-again, maybe-now-maybe-later administration wobble over whether to sell high-technology AWACS aircraft to Saudi Arabia is not quite of the magnitude of the Kennedy administration's early effort to invade Cuba and overthrow Fidel Castro with Cuban exiles and supposedly covert American support; the consequences don't figure to be a cataclysmic -- or as tragic.

But the damage to the new administrations's reputation for reliability and competence to conduct foreign policy coherently and decisively is going to be considerable, one way or the other -- the more so since precisely these virtures were so loudly laid claim to by the Reagan crowd as examples of what would wonderfully new and different about the Reagan presidency.

I say "one way or the other" because damage limitation is all that's left to the administration. While still in the hospital early this month, President Reagan was pressured by the Pentagon and Defense Secretary Casper Weinberger into deciding to wrap five AWACS for Saudi Arabia into a package of other items including fuel tanks, missiles and refueling aircraft to "enhance" the performance of 62 F15 fighter bombers, already approved for sale to the Saudis by the Carter administration in 1978. Both houses of Congress can veto such transactions within 30 days.

This provoked a storm of protest from the Israelis who already felt betrayed. They thought they had a firm American promise not to "enhance" the F15s, so there was talk at State and the White House of removing the AWACS from the package and delaying the submission of that deal to Congress. Now a formal compromise has been reached. The orginial package will go to Congress. AWACs included, but perhaps not until after Israel's June 30 election. This is not likely to reassure either the Israelis or the Saudis. For the congressional battle is likely to be no less fierce, and the outcome no less uncertain, by being delayed.

Secretary of State Haig, the voice of prudence in this matter, has it on the authority of a private letter from Sen. Robert Byrd, leader of the Democratic minority, that Awacs-for-Saudi Arabia "is certain to spark even greater controversy in the Senate" than did a similar offer to the shah of Iran in 1977. That transaction survived Congress. But only the fall of the shah in advance of the delivery date early this year prevented the airplanes from falling into the hands, conceivably, of the present Iranian government -- or one still less congenial to U.S. interests.

Byrd's three-page letter to Haig raises precisely that point about the proposed Saudi deal. "Since this would be the first poetential delivery of AWACS to a non-NATO country," he writes, "I am most concerned over potential secuirty risks which could compromise a technology the Soviets are years away from perfecting."

After posing a series of technical questions about exactly what sort of electronic equipment the Saudi AWACS could be carrying, Byrd zeroes in on the principal source of Israeli concern. The "A" in AWACS stands for "airborne" and the "W" for "warning." (The "S" stands for System.) But a fully equipped AWACS is more than a defensive reconnaissance aircraft with super-sophisticated eyes and ears, capable of giving early notice of air attacks or troop movements or mobilization on the ground.

The "C" stands for "control" -- the capacity direct offensive operations, "What impact would the sale of AWACS to Saudi Arabia have on the military stability in the region?" Byrd asks. "In another Middle East war, what capability would AWACS give Saudi, Syrian and possibly Jordanian air forces?. . . Would this require significant purchases of counter-measures on the part of Israel?"

Now, Sen. Byrd is not generally in the vanguard of Israel's Senate supporters. But he is a powerful force among the Senate's Democrats His strong doubts about AWACS for the Saudis make it all the more likely that the administration could well lose in Congress.

And that, as Haig recently argued, "would represent a grievous setback in American relationships with Saudi Arabia."

Or, at great cost, the administration might win, which, given the high and rising pitch of Israeli protest, would result in at least as greivous a setback in American relations with Israel.

It's a mess, for which you can blame the American military for having forced the pace. But the root cause of the Bay of AWACS runs deeper -- to the workings of the policy-making machinery itself. The Reagan administration in April 1981 is not much closer than the Kennedy administration was in April 1961 to installing a system for making national security decisions that is reasonably fail-safe.