Secretary of Defense Caspar Weinberger's proposal to base the MX missile in airplanes has triggered President Reagan's first defense crisis, threatening highest-level Air Force resignations and a bipartisan revolt by defense leaders in Congress.

The defense community was flabbergasted by the result of Weinberger's long, soul-searching study of how to make the mobile MX missile invulnerable to Soviet surprise attack. Reagan supporters in both the Pentagon and Congress fret that Cap has knifed the Republican Party's pledge for the "earliest possible deployment of the MX in a prudent, survivable configuration." Those words, specifically cleared by candidate Ronald Reagan, were written into the 1980 party platform.

If Reagan and Weinberger succumb to pressures building against the air-based MX system, more months of delay to decide on a substitute are certain. But if they stick to Weinberger's favored system, they will confront not only those Air Force resignations but an informed opinion within the defense community that no air-based system can be truly invulnerable.

Why Weinberger has selected the most costly and least effective MX option is unanswerable in technological terms. The suspicion is that Reagan, under pressure from Western state Republicans, ruled out the Carter land-based system. Whatever the cause, the president faces a political crisis over the nation's strategic security.

This danger was brought straight to the Oval Office Aug. 6 when Sen. John Tower, chairman of the Senate Armed Services Committee, had his first serious MX talk with Reagan as president. With Weinberger present, Tower gave this carefully considered warning: Congress never will by the air-based MX.

At almost the same minute, Reps. Melvin Price of Illinois and William L. Dickinson of Alabama, chairman and senior Republican on the House Armed Services Committee, were sending a letter to Weinberger. The air-based system has "no congressional support," they wrote. Dickinson went to the White House to slip a copy of that letter to the president.

At the Pentagon, no public revolt of the air generals is likely, but the administration faces embarrassment. At least two top Air Force officers, Lt. Gen. Kelly Burke and Maj. Gen. Guy Hecker, will quietly take early retirement if the air-based system is chosen. Burke has confided to friends that his retirement would be dictated not by a desire to fight the decision or "go into the streets," but because he could not testify to Congress as an advocate.

Intimates report that Gen. Lew Allen Jr., the Air Force chief of staff, is also prepared to quit if Weinberg sticks with the air-based system. Allen and the top echelon of the Air Force are convinced that putting the MX into C5 cargo planes ready for instant takeoff would subject America's ultimate security to the same hazards that always have made bombers vulnerable.

Weinberger only recently removed the MX gag he imposed on the Air Force early this year. That gag was designed to give Weinberger running room on the MX obstacle course without Air Force pressure.

But the gag may have cost Weinberger information he needed. The Carter administration's secretary of defense, Harold Brown, in late 1978 flirted with an air-based MX option, with some Air Force backing. But the more it was studied, the worse it looked. A secret Air Force memo to the White House in the spring of 1979 termed it "inferior" to a land-based system, which then became the Carter administration's choice.

In Weinberger's defense, he has been under great political pressure from Reagan to leapfrog and discredit earlier studies.

All those studies concluded that only a politically troublesome land-based system would offer maximum security. Apart from Western state pressure, Reagan and his political advisers did not want to be tainted with Carterism in making the first important defense decision of his presidence.

Weinberger is caught in a trap, with time running out. He is trying to persuade the Townes Committee, a group of specialists he named to advise him on the MX, to underwrite his airbased preference, but the committee wants a land-based system. Now he has been warned that if he does not change his mind, Congress will repudiate him.

That may be overstatement, considering Reagan's way of getting what he wants from Congress. But what Reagan and Weinberger ought to want is nothing less than the best system to make America secure, whatever the original patronage or the political hazards. That's what candidate Reagan promised. But seven months of his presidency hve only brought him political crisis and not yet one hard step toward protecting the country's strategic security.