It is a cliche to say that September 11th changed the world, yet in some ways such talk is true. Russian/American relations have changed fundamentally, as Russia's quiet disappointment at America's decision to withdraw from the Anti-Ballistic Missile Treaty (ABM) shows. The surprise is that it took Osama bin Laden's terrorists to reveal that no fundamental differences of ideology, economics, or politics now exist between the two countries.

Russia experienced international terrorism long before others and thus sought joint international efforts against it long ago. Indeed, America did not lure Russia into the current war in Afghanistan; instead, Russia is using the US to rout bin Laden's terrorists and the Taliban, who caused instability across Central Asia, Chechnya, and other Russian regions.

So the new Russia/US relationship is not one of unilateral Russian concessions, as so many people here claim. It benefits both sides. With Al Qaeda and the Taliban routed, Russia's southern borders will be safer. Moreover, it is no exaggeration to say that Russian assistance - political, military, technical and intelligence - is equal in importance to the US as the support provided by its NATO allies altogether (excluding Britain).

None of this excites euphoria here. Many Russian analysts argue that once America's war against the Taliban is over, it will return to its unilateralist ways when help is no longer needed. This is a possibility. So, for today's altered Russia/US relations to flourish, two things are needed:

$an agreed, negotiated framework mapping the common interests of the two countries;

$a mechanism for joint decision-making to protect these interests.

A first practical step to be taken here is to establish a common definition of international terrorism. For example, are Basayev and Khattab, the Chechen rebel leaders, terrorists? What about the Kosovo Liberation Army? Agreement on this may be hard to find, but must be sought.

We must pursue common efforts that do not demand an enemy to unite us. Joint efforts against the proliferation of weapons of mass destruction - nuclear, chemical and biological - offer an opportunity here. Greater economic cooperation, particularly over development of Russia and Central Asian oil, offer another. Regrettably, this still seems a dream because of differing interests over oil exploration and oil prices, as well as Russian debt repayment.

The latter problem is vital. Debts burden Russia's economy mightily, which will become heavier as oil export revenues fall. Russia's foreign debts should be restructured and part of them - say, the Soviet-era debts - should be written off. A positive sign here is the recent decision by the foreign relations committee of the US Senate to write off a large part of Russia's American debts.

Some within Russia view this decision as a reward for Russian calm after America unilaterally withdrew from the 1972 ABM Treaty. The truth is that the Senate committee reached this decision even before America announced its withdrawal. In any case, no legislation on this matter has been written and it remains unclear what conditions will be imposed. Nor is it clear that the US will convince Europe to follow suit. This matters because Russia's debts to Europe are greater than those owed to America.

Much of the pre-September 11 agenda also remains unaddressed: arms control, NATO enlargement, and Russia's integration into the global market. America's unilateral withdrawal from the ABM Treaty will likely make finding agreement on all these issues harder. Scuttling the ABM Treaty might also inspire Russia to seek its own free hand on nuclear issues.

For example, the START II Treaty of 1993 requires both countries to cut their strategic nuclear arsenals in half from the 6,000 warheads permitted under the START I agreement. Abandoning START II would allow Russia to fit three nuclear warheads to each of its new, single-warhead Topol-M missiles. This is important because land-based nuclear missiles form the core of Russia's strategic forces. With START II in effect, Moscow would need to deploy large numbers of Topol-M missiles or build nuclear submarines equipped with ballistic missiles to match America.

This need not happen if President Bush, as promised, cuts America's arsenal by two-thirds - to between 1,700 and 2,200 warheads - to match President Putin's planned cuts. But President Bush doesn't want to write this promise into a formal treaty - indeed, America's president seems allergic to formal treaties, whether they tackle pollution or nuclear weapons. But without a formal treaty, a new nuclear buildup may occur through carelessness, not superpower rivalry.

Although President Putin won't make any sudden moves to destabilize Russia's newfound friendship with America, he must still defend his country's security. What he might choose to do is to follow America's example, so that, without officially renouncing the START treaties, Putin may quietly decide that he no longer considers himself bound by some of their provisions.

Despite the ABM Treaty setback, the new Russia/US and Russia/NATO relationships must be institutionalized within treaties and new collaborative mechanisms. But America and its European allies sign formal treaties all the time and still remain friends. Thus American unwillingness to reach formal agreements raises suspicions here that it wants to use today's cooperation as camouflage for renewed unilateralism. In particular, it is feared that the Bush administration wants to escalate the anti-terrorist war by spreading hostilities to states America denounces as "rogues." To do so would not only destroy the anti-terrorist coalition, but harden anti-American sentiments everywhere, including within Russia.