Justice Lewis F. Powell returned to the Supreme Court last week after a long period of recuperation from surgery. His absence focused attention on the justice's rather remarkable role on the tribunal: He is, more than many had realized, the pivotal decision-maker, the justice whose vote in close cases is almost always the decisive one. Post reporter Al Kamen noted the other day that of the 62 cases already decided this term, the court was divided 5-4 on nine occasions. Justice Powell was in the majority eight times. Four other cases, which were heard during his absence, have been scheduled for reargument, presumably because Justice Powell's vote is needed to make a majority. And seven other cases were decided on a 4-4 tie, which affirms the ruling of the lower court but has no value as precedent. Justice Powell's vote would have broken these ties.

There is much that is admirable about ideological justices whose positions on a given issue are firmly held and easily predicted. Often such a pattern indicates great strength and personal integrity. But the role of the pivotal justice is equally fascinating. Some who cast frequent swing votes may simply reveal an indecisiveness that is unseemly in a judge. Others, like Justice Powell, appear to come to each case without preconception, approaching each issue within a framework of principles, personal philosophy and legal precedent, but willing to hear both sides with attention and respect. This role is a demanding one, for it requires intellect, objectivity and the determination to consider every case as unique.

In a court as closely divided as this one, the justice at the center is critically important. An examination of this year's cases and the importance of Justice Powell's vote -- or his absence -- emphasizes his influence at the center of the tribunal. It also reminds us that the balance of power there is fragile and that one of President Reagan's greatest opportunities to shape the future will likely be in that forum.