IF PRESIDENT REAGAN completes his second term it is expected he will have appointed over half the federal judiciary. That is no surprise: a federal judge serves 15 years on average, and the president's appointments will be made over eight years. But it's a lot of judges, and the manner of their confirmation could be improved.

Last year, Democrats on the Senate Judiciary Committee complained that judicial nominations were coming too quickly, without sufficient time to consider each one carefully. In October alone, there were hearings on 16 nominations. Now, committee chairman Strom Thurmond has agreed to new rules designed to give the minority more time to investigate, particularly in controversial cases.

How should committee members use that time? Common Cause offered its ideas in a recent study on the confirmation process. Some of its suggestions are dubious. Beefing up the committee staff with investigators, for example, is not the answer. Field investigations have already been done by the FBI, the nominee's peers in the legal profession have made studies, and senators from the nominee's state have had an opportunity to make a judgment before a nomination is sent to the Hill. It isn't practical either to urge the committee to notify all sorts of groups with a possible interest in the nomination. Judicial appointments are publicly announced and well reported. Those with comments to make have an obligation to contact the committee, not the reverse.

But it makes sense that the American Bar Association be asked to provide far more information. Now the ABA simply declares that a nominee is "exceptionally well qualified," "well qualified," "qualified" or "unqualified," without giving reasons. A more complete analysis would be helpful. Senators should also share responsibility for overseeing the confirmation process. The Democrats have now assigned their most junior member -- the only non-lawyer on their side -- to this task. Finally, the committee should issue written reports on nominations for the use of the full Senate.

The are now more than 50 vacancies in the federal judiciary. The Senate has a demanding job ahead in evaluating the men and women who will be proposed for these lifetime appointments. Broad cooperation to devise the best procedures for this work is essential.