For a supposedly fading president, Ronald Reagan is doing reasonably well in dealing with his enemies. But as the old saying goes, he is having a devil of a time protecting himself from his friends.

As his second term closes in on him with few foreign policy successes to his credit, Reagan is trying to leave a constructive legacy. He has shown a new willingness to consider a negotiated settlement in Nicaragua. And he has backed away from previous demands for intrusive on-site verification of a U.S.-Soviet treaty that would eliminate medium- and short-range nuclear missiles in Europe and Asia.

Reagan's retreat from a verification plan that most experts have long considered unnecessary gives him a chance, for a change, to regain the public relations advantage on arms control from Soviet leader Mikhail Gorbachev. Coupled with West German willingness to scrap 72 aging Pershing missiles, Reagan's verification realism probably means that the "double-zero" treaty will be signed at a superpower summit in the United States this November.

The proposed treaty is a modest achievement compared with the grandiose fantasies of eliminating strategic nuclear arsenals indulged in by Reagan and Gorbachev at the Reykjavik, Iceland, summit last year. But it is a worthwhile step to rid the world of a significant category of deadly nuclear weapons. It would be particularly sweet for Reagan, who remembers that the double-zero plan was widely derided when he first offered it in 1981.

Both the proposed treaty and Reagan's dalliance with a Central American peace plan have been greeted with horror by the noisy right wing of the president's constituency. These objections have been given added weight by the skepticism of former secretary of state Henry A. Kissinger, who has expressed concern that the treaty would strip Europe of the U.S. nuclear umbrella that has shielded it from potential Soviet aggression since World War II.

The Reagan administration has a good response to this argument. The United States would still retain sufficient sea- and air-based nuclear weapons to protect Europe once the land-based missiles were removed. Reagan can also remind his critics that the U.S. missiles that would be withdrawn under the new treaty were installed only because of an alarming buildup in Soviet medium-range missiles that will now be dismantled.

Such arguments are not likely to sway right-wingers who suspect that Reagan is about to sell out his ideological birthright for a place in the history books. Perhaps Reagan could gently counter that anything opposed by their old adversary Kissinger can't be all bad. But a sense of humor is not the strong suit of "movement conservatives" who view the signing of any agreement with the perfidious Soviets as a betrayal by their hero Reagan.

The fallback position for those unwilling to acknowledge that Reagan actually believes in arms control is to blame White House chief of staff Howard H. Baker Jr. or First Lady Nancy Reagan for the villainy of administration arms-control efforts. On this issue the right and left make common cause in taking up the view that Reagan is a disengaged president who displays leadership only with a script in hand.

It is unfair for critics of Reagan's arms-control efforts to have it both ways, even if this complaint can also often be justifiably made about Reagan. The Iran-contra hearings revealed that the president was the driving force behind the ill-conceived scheme to trade U.S. weapons for American hostages. Reagan was so obsessed with the idea that he ignored his promises not to deal with terrorists, as well as the advice of experienced Cabinet officials.

The president deserves the full blame for this botched episode -- but he deserves an equal amount of credit for persisting in an arms-control proposal that also obsesses him. Reagan has shown himself to be a risk-taker, for better and for worse, and the risks in this case are worth taking. It is an irony that those who celebrated Reagan's leadership when he had little of substance to show for it have turned on him when he seems on the verge of real accomplishment.

Reaganism of the Week: Speaking to the Town Hall of California last Wednesday, the president said, "They told me that I came on from the left and I can exit from the right. That's been the story of my life."