When Ronald Reagan proposed sharing missile-defense technology with the Soviet Union in 1986, Mikhail Gorbachev scoffed at the idea. More than 20 years later, however, Russian President Vladimir Putin is rethinking this hasty rejection.

Or so it would seem. At last week’s G-8 summit in Germany, Putin surprised President Bush with a suggestion to incorporate a Russian radar located in Azerbaijan into a prospective missile-defense system whose main purpose is to protect North America and Europe from an Iranian nuclear threat. The offer comes after months of saber-rattling, in which Moscow expressed strong objections to U.S. plans to build its own radar in the Czech Republic and base ten anti-ballistic missiles in Poland. Just days before the G-8 meeting, for instance, Putin talked about retaliatory measures, such as aiming Russian warheads at sites in Europe. One purpose of such blustery rhetoric has been to turn European public opinion against missile defense.

Bush immediately labeled Putin’s Azerbaijan proposal “interesting,” which is true enough. If it is indeed a serious offer to enhance global security against the menace of ayatollahs who brandish nuclear weapons, then it could represent a geopolitical breakthrough. Yet if it is just another Russian attempt to undermine existing missile-defense plans, it deserves to be shot down quickly.

There are plenty of reasons for skepticism. A main Russian objective appears to be keeping interceptors out of Europe entirely — at a news conference on Friday, Putin suggested basing them in Turkey, or perhaps even in Iraq or at sea. Yet as Secretary of State Condoleezza Rice has pointed out, missile-defense placements are fundamentally about geography and geometry. Interceptors are built to meet their targets at certain points in their flight paths. That makes some launch sites better than others. From the simple standpoint of targeting an Iranian long-range missile as it flies toward London or Paris, Poland is probably much preferable to alternatives.

What’s more, if Russia were fully determined to counter the Iranian nuclear threat, it could take helpful diplomatic steps right now. Moscow might suspend all nuclear cooperation with the ayatollahs, sever some of its commercial ties, and support tougher sanctions at the United Nations. It has pursued none of these strategies so far because of powerful economic incentives and a refusal to see Iran as an international hazard. Genuine Russian cooperation on missile defense would be welcome, but it would not come to fruition for years — and even then it would merely counter a set of problems that Russia is complicit in creating.

Russia’s determination to block the missile-defense sites in the Czech Republic and Poland always has seemed to have more to do with exerting influence over Eastern Europe than with anybody’s security interests. Ten interceptors are no deterrent to Russia’s missile arsenal, which would easily overwhelm them. One potentially legitimate Russian concern is that the destruction of an Iranian missile could take place above Russian territory, leaving its people vulnerable to any debris or fallout. Yet the answer to this problem lies in measures that discourage Iran from launching in the first place. The best missile-defense system, after all, is one that doesn’t ever have to be used.

A system that integrates a radar in Azerbaijan, so close to the border of Iran, would be more robust than one that didn’t. If Putin’s proposal offers tools that will enhance the security of North America and Europe, then it should receive frank consideration. Full partnership in such a missile-defense plan certainly would make sense for Russia: Not only would it improve the currently chilly relations with the United States, but it potentially would protect Russia itself from Iranian provocations. Finally, if negotiations go forward, the United States should begin from a position of strength: Congressional Democrats must agree to restore the funding that they’re currently trying to cut from the Eastern European missile-defense sites.

When it came to dealing with the Soviet Union, Reagan often encouraged a policy of “trust but verify.” Putin’s missile-defense proposal calls for a slightly different approach: Verify Russia’s intentions, and only then begin to trust.