IT'S not the most glamorous of arms- control efforts. But in years to come the "Open Skies" treaty signed this week in Helsinki may rank in importance with the START strategic arms pact and other milestones of post-cold war geopolitics.
First suggested by the United States in the pre-spy satellite days of 1955, Open Skies calls for unhindered surveillance plane flights through the airspace of signatory nations. With 24 nations already signed up (more may follow), the territory now open to aerial inspection stretches from Vancouver to Vladivostok.
"It is the most wide-ranging international effort to date to promote openness and transparency in military activities," claims a State Department summary of the treaty.
Open Skies' original purpose of lessening superpower nuclear tensions may seem much less important than it has in decades past.
But new flare-ups behind the old Iron Curtain and worries about the whereabouts of ex-Soviet nukes only emphasize the value of confidence-building reconnaissance measures.
"When you think about what starts wars, it's not numbers of weapons. It's what one nation thinks the other will do," says Amy Smithson, a senior associate of the Henry Stimson Center and co-editor of a book on Open Skies.
"In an age with so many tensions around, an age of ethnic conflicts and massive political changes, we all want to know that conventional as well as mass destruction weapons are being handled responsibly," adds Ms. Smithson.
Open Skies was originally proposed to the former USSR by President Dwight Eisenhower at the Geneva Conference of 1955. The Soviets weren't interested, and the idea went nowhere.
Repackaged and expanded to a multinational proposal, Open Skies was put forward again by President Bush in 1989. Formal talks opened in Ottawa in 1990, and despite high hopes quickly stalled.
Only in the wake of the Soviet coup attempt did productive discussions begin, with negotiators from the then-intact USSR agreeing that all their territory should be open to inspection.
Final agreement was reached last week by negotiators in Vienna. The formal Open Skies pact was signed in Vienna on March 24 by foreign ministers in Helsinki at a meeting of the Conference on Security and Cooperation in Europe.
The pact's founding signatories include the members of NATO, the former Warsaw Pact nations of Eastern Europe, Ukraine, and Belarus (formerly Byelorussia), signing together as a successor to the USSR.
Diplomats expect that other former Soviet republics may sign up shortly, as some had observer delegations at the final talks.
Each signing nation has been assigned a quota of overflights by other nations that it will be obliged to accept.
The quota varies roughly according to size: for both the US and Belarus, it is 42. For Germany, France, Britain, and Italy, the number is 12. For smaller participants - Hungary, Iceland, Bulgaria - the quota is four overflights.
In practice, the number of flights that will actually be conducted over a nation in any given year, plus the identity of the nation that will do the overflying, will depend on the worries of particular countries plus the international situation at the time. As the State Department summary dryly notes, there is at present little interest by anyone in flying over the United States or Canada. Conversely, "there is relatively intense interest in observing the situation in the area of the former Soviet Union. "
To start with, the US will be allowed eight overflights of Russia and Belarus, and will share an overflight of Ukraine with Canada. For the most part, other treaty signatories will be overflying not so much superpowers as their own immediate neighbors. Hungary, for instance, will be allowed one flight over Romania, and one over Ukraine.
In later years this dividing of quotas will be carried out by a new Open Skies Consultative Committee, to meet in Vienna.
The planes used in Open Skies can belong to either the overflying nation, or the host nation. It's the hosts' choice, though on this point only Russia has indicated it might force other nations to fly over its territory using Russian planes.
To begin with, the only sensors allowed onboard the surveillance planes will be cameras sharp enough to distinguish a truck, say, from a tank.
After a three-year phase-in period both Synthetic Aperture Radars and infra-red sensors will be allowed, to complement cameras and permit data gathering at night and in bad weather.
Data will have to be shared between flyer and host. And all information will be available - for purchase - to all treaty signatories.