THE QUESTION before the Senate was

whether it found Sandra Day O'Connor qualified to serve on the Supreme Court. Since Judge O'Connor's qualifications were obvious, the Senate's confirmation yesterday of her nomination was a forgone conclusion. But the overwhelming vote, 99 to 0, was also an acknowledgement that the nomination of a woman to this court was overdue.

Her confirmation ends a tradition of exclusion that was destitute of any justification except sheer habit. As she takes her place, Justice O'Connor will demonstrate to other women who are lawyers that the pinnacle of their profession is no longer arbitrarily closed to them. It is the kind of symbolism that is central to the life of the country, and both President Reagan and the Senate are entitled to great credit for this appointment.

The president chose his candidate well. He clearly wanted a nominee with a conservative inclination and preferably with some political experience as well. But beyond that, there aren't many questions that a president, or a Senate Judiciary Committee, can ask about a nominee's views. On all the questions relating to future decisions, they can only trust to the candidate's judgment and character. That was a matter of some considerable exasperation to several of the least experienced members of the Judiciary Committee, as they pressed her in one or another attempt to commit her to their various political positions. She turned them all aside with an impressively skillful courtesy.

Justice O'Connor has made it clear that, generally speaking, she would prefer a restricted role for the courts. But judges haven't the luxury of working in terms of general preferences. They have to decide specific cases. Like everyone else in public life, judges have to respond to events. There have been times in the recent past, most notably in the racial desegregation and voting rights cases, when a highly restricted view of the court's responsibility would have worked out badly for the country and damaged the regard in which it holds the basic law under which it lives. To what extent that will be true in the future is a question that only the future can answer. For the present, it is enough to know that Justice O'Connor has already demonstrated a degree of ability and balance that promises to serve her, and the court, well.