THE STOCK MARKET'S wild leap upward brings a sudden message of good cheer to an economy that had seemed trapped in its own sense of gloom. People who work at the White House will tend to give credit to President Reagan's speech Monday night. People who work in lower Manhattan will more generally attribute it to Henry Kaufman, the oracle at Salomon Brothers, who is widely considered in that neighborhood to be endowed with magical powers.

There are many people who will regard either explanation as unpersuasive, and who will take this event as further evidence that the market is always a little crazy. But it's true that the market has been lower, and interest rates much higher, than any previous experience could easily explain. Perhaps we are seeing the beginning of a long overdue process of correction. Interest rates have been declining rapidly. To keep up this momentum, it becomes all the more important for Congress to continue moving the tax bill toward passage.

Last August, the markets' behavior deeply dismayed the Reagan administration. The president had expected his big tax and budget bills to be received there as a pair of triumphs. But instead of falling smartly as Washington had expected, interest stayed sky-high, and the same Mr. Kaufman spoke of "an atmosphere heavy with apprehension" about the federal budget, inflation and all the rest. Over the following months, the country seemed to fall into a mood of deep pessimism that made every setback worse. Perhaps, for reasons not necessarily strictly economic, we are now beginning to see a change in more than the interest rates.