THE AIR TRAFFIC controllers' strike is a wildly misconceived venture that deserves the government's extraordinarily severe response. A strike against an essential public service is always wrong in principle. In this case, it is also illegal, and the controllers' attempt to demolish the law by a massive violation is doubly wrong.

The controllers say, correctly, that they do exacting work under conditions of stress. The $40 million settlement that their union originally accepted doubtless seemed reasonable to most people. But the controllers rejected it and struck for benefits that would, by their own accounting, cost more than half a billion dollars a year.

Half a billion dollars? The controllers seemed to have departed from what the rest of the world calls reality. A raise of $10,000 a year for each controller, along with shorter hours and earlier retirement? On the week after Congress voted, by large majorities, the biggest cut in the history of the federal budget, with reductions in a long list of welfare and Social Security benefits? The controllers don't seem to comprehand that they will have to turn to the same Congress for their pay raises.

Nor do the controllers seem to understand the position in which they have put President Reagan. He has just bet his presidency on his economic program. But interest rates won't come down until people see inflation coming down, and economic analysts are currently warning their clients that there's not much evidence yet of any change in the underlying rate of inflation. That underlying rate is, essentially, the rate at which wages are rising. The money markets are watching wage settlements with fixed attention.

If one union, whose members work directly for Mr. Reagan, were now to achieve a spectacular wage increase through an illegal strike, that would be the end of the Reagan economic program. Investors, bankers and borrowers would all immediately conclude that, whatever its rhetoric, the Reagan administration was not serious about reducing inflation. That's why Mr. Reagan now has to stand absolutely fast.

The controllers' union is small, as unions go. But that makes no difference. In the summer of 1966, an aircraft mechanics' strike exploded President Johnson's wage guidelines and, with them, the last serious attempt by the Johnson administration to hold down inflation. That was also a small union. But its strike, like the present one, was highly visible, disrupting air travel at the height of the summer vacation season. Perhaps the controllers remember that strike. They can safely assume that the White House remembers it, too.