THE EFFECTIVENESS and constitutionality of the independent counsel law may not seem to be in doubt, but that perception is wrong. Within the last month, two significant events occurred that strengthen public perceptions that the law is working well: Michael Deaver was convicted of perjury in the first case ever won by an independent counsel, and the law was slightly amended and extended for five years by Congress. But the president, who was initially opposed to an extension, had a word of caution at the signing ceremony. He reminded legislators that the courts had yet to rule finally on the law's constitutionality.

A series of challenges to the law was filed in 1987, but the only one now proceeding through the appeals process is that initiated by three former Justice Department officials challenging the authority of an independent counsel to investigate their conduct. In July Chief Judge Aubrey Robinson of the U.S. District Court here ruled against the three and held the law to be constitutional. That ruling was appealed, and the U.S. Court of Appeals heard arguments Sept. 16.

Under ordinary circumstances, a three- or four-month delay between an argument in a case and the court's decision would be unexceptional. This case is an important one, and a number of amicus briefs were filed, including those by Congress, the Justice Department, the American Bar Association, two other independent counsels and a number of public interest groups. Thoughtful consideration is required. But in this case the judges themselves acknowledged that a quick decision was needed. During the oral argument in September, the court assured the litigants that the case would be handled on an expedited basis.

It is important that this promise be kept. There are about a half-dozen independent counsels at work now. Some have been conducting investigations for more than a year. One man has already been convicted and another indicted, and additional prosecutions are expected early this year. It is unfair to the prosecutors and their staffs, to the taxpayers and most of all to the targets of these investigations to continue such proceedings indefinitely without a ruling on constitutionality. The question must eventually be decided by the Supreme Court, but the case can be argued and decided there this term only if the court of appeals reaches its decision soon. Otherwise, a full year could be lost. The appellate court should make this case a matter of high priority in the new year