IN VOTING TO override President Reagan's veto of a supplemental appropriations bill last week, Congress reminded the president that there is such a thing as asking for too much. Whether or not the override marks a permanent reversal in congressional willingess to go along wit the administration, it is certainly an important signal that Congress cannot be counted on indefinitely to pull the administration's chestnuts from the fire while the president keeps fanning the flames.

Congressional patience has been running out ever since the legislators woke up to the fact that, in accepting the president's initial tax and budget packages, they were also taking home enormous budget deficits for the forseeable future. Worse yet, the president's February budget had made clear that the administration itself had no politically feasible idea of how to narrow those deficits. All that might have been acceptable had the president not continued, unabashedly, to campaign for a balanced budget while lambasting Congress for its failure to do what he himself could not.

Despite this obvious entrapment, Congress has behaved most responsibly. Without presidential leadership, it fashioned and adopted a series of difficult budget cust. It also developed and enacted a landmark tax bill that not only supplied much-needed revenues but made some long overdue reforms in the tax system. Now and then, Congress has gotten fidgety when the president pressed for the last measure of compliance on appropriations bills, but until now no veto by President Reagan has been overridden except on a copyright matter.

This time, however, the president went too far. The supplemental appropriations bill that he vetoed -- and that will now become law -- is not only well within the limits set by the budget resolution. It actually means spending almost $2 billion less than the president had requested. If Congress was guilty of "budget-busting," as the president maintained, Mr. Reagan himself was $2 billion guiltier.

Nor were congressional tempers improved by the president's insistence that Congress trim almost $1 billion from popular social programs while supplying an additional $2 billion for certain relatively low-priority defense items. With $200 billion already sloshing around in the Pentagon's coffers this year, asking for more money for items like travel seemed more than merely excessive. It also fed suspicions that the president was more interested in striking a militant pose than in building a well-balanced defense.

In many ways, Congress has done the president a favor. The resurrected bill does provide the president with some things that he wants very much -- such as money for his Caribbean Basin Initiative and an additional half-billion dollars for defense -- that might well have been dropped in a subsequent compromise. And the president has been given a timely reminder that, while presidential leadership can be very important in determining policy, the Constitution gives the power to write laws to Congress.