THE REPORT of the House and Senate select committees on the Iran-contra affair does more than add useful detail and context to earlier accounts of the Reagan administration's darkest passage. It takes on a special authority from its tone of factuality and restraint and from its approval by a bipartisan majority, including Republican Sens. Warren Rudman, William Cohen and Paul Trible Jr. The report is a devastating portrait of the way secrecy, deception and ''disdain for the law'' produced a fearful policy breakdown, pushed elements of the administration into a moral and political jungle and savaged the president's personal authority in ways from which he has still not recovered.

Mr. Reagan avoided direct comment on the report, and the White House sought in effect to acknowledge it and move on. One can understand why the administration would not want to revisit the scene of repeated policy and process horrors and, it may yet turn out, assorted crimes.

The worst thing that comes out of the report is the lying: the lying done to the president, the secretaries of defense and state, Congress and plenty of others, not least the public. No claim is made in the report that Mr. Reagan himself knowingly lied. But in undertaking to swap arms for hostages with Iran, a policy he could not or would not try publicly to justify, he created the conditions for a policy that could only be pursued -- and later covered up -- through deceit.

Confronting the pervasive contempt for democratic process and law, the committees concluded there is no magic legislative remedy. Their report suggests tinkering a bit with the relevant statutes and procedures. It sounds sensible enough, but in fact a more effective remedy may be available in the governmental and political arenas. Officials in both branches and at all levels must carefully tend the system that endows them with power. The report, documenting, as it does, the terrible consequences of officials' acting in the opposite way, makes it all the more essential for the president to do what he still has not done: find an effective way to acknowledge the immensity of the misdeeds that took place and the derelictions of the people who abused the power and trust he gave them.