Prime Minister Pierre Trudeau once famously derided the "nuclear accountants" and the arcane counting rules that typically accompany nuclear arms control efforts. He had a point -- but the nuclear accountants are back because, happily, nuclear arms control has returned to the public policy agenda with sufficient prominence to once again require their exacting services.

The United States currently has either 5,576 nuclear warheads, or it has 2,200, or 9,400. All three numbers are, in fact correct. It's all in the accounting.

The first number represents the total warheads tallied under the counting rules of the 1991 Strategic Arms Reduction Treaty (START). START accounting is focused on strategic (long-range) delivery vehicles, and the U.S. reported in April that it has 550 land-based intercontinental ballistic missiles, another 432 missiles on 14 submarines, and 216 long-range bombers -- and, together, these missiles and aircraft are capable of carrying 5,576 warheads. So under START that is the relevant number, whether or not that many warheads are actually deployed. The point is they could if they chose to.

The 2,200 warhead figure is based on the 2002 Strategic Offensive Reductions Treaty (SORT), also known as the Moscow Treaty. That treaty has no verification provisions and does not require the reductions to be permanent, so it is less like a treaty and more like a general U.S.-Russian joint statement of mutual policy intentions to reduce actively deployed strategic warheads to 2,200 by 2012. Since the U.S. has reported that through deployment adjustments it is reaching the SORT targets ahead of schedule, 2,200 becomes the relevant number.

And the 9,400? That includes the large number of warheads in storage, many of which are scheduled to be dismantled, but for the time being remain in the nuclear inventory. It also includes all tactical or nonstrategic warheads, only some of which are deployed. The details are not officially disclosed, but the best estimates of the nuclear accounting community put the total number of deployed and in-storage warheads of any type in that 9,400 range.

The Russian numbers are roughly similar, but now the U.S. and Russia have agreed on the ambitious objective of negotiating a new START treaty in time for the Dec. 5 expiry of the current one. It will succeed the 1991 treaty, supersede the 2002 Moscow Treaty, and will introduce a whole new set of numbers.

To that end, presidents Barack Obama and Dimitry Medvedev have signed a joint statement of understanding instructing their negotiators to cut deployed strategic warheads to between 1,500 and 1,675, and cut delivery vehicles down to 500 to 1,100.

Thus, the new treaty will replace both the 5,576 number and the 2,200 number with a maximum of 1,675. That's real progress, but it's only a beginning because the big number -- the 9,400 figure that includes strategic warheads in storage and all tactical warheads -- will not be immediately affected by a new treaty. That 9,400 will continue to decline in the normal post-Cold War process of gradually dismantling surplus warheads, but it won't be seriously reduced until treaty accounting applies to all warheads - strategic and tactical, deployed and those in storage. When all warheads are subjected to legally-binding limits and the 9,400 becomes 1,675 we will have made genuine progress.

And all warheads will have to be subjected to treaty limits for nuclear weapon states to live up to the principle of "irreversibility" that they all agreed to in 2000 at the review conference of the treaty on the non-proliferation of nuclear weapons (NPT). Irreversibility means essentially that any warhead or delivery vehicle not specifically sanctioned, and thus counted, in arms control treaties must be verifiably and permanently dismantled and destroyed.

Another basic principle that will have to guide nuclear arms control going forward is transparency. A high level of compulsory openness is required to foster confidence as well as accountability. Reliable transparency will also require international monitoring mechanisms to complement U.S.-Russian bilateral verification arrangements as a means of establishing accountability to the entire community of states - and to use accounting methods that spread light, and not fog, over the enterprise.

Both Obama and Medvedev have joined a broad range of prominent public figures, including former U.S. secretary of state Henry Kissinger and former Soviet president Mikhail Gorbachev, in affirming that the formal goal of nuclear arms control must be permanent disarmament and a world without nuclear weapons. So a new START agreement will necessarily be the start of something new. The first agreement will have to be followed by further agreements and steady reductions in the levels of permitted warheads with commensurate restrictions on delivery systems -- but, as Kissinger put it in 2007, arms control action must necessarily be guided by the vision of a world without nuclear weapons.

"Without the bold vision, the actions will not be perceived as fair or urgent," he said. "Without the actions, the vision will not be perceived as realistic or possible."

Ernie Regehr is co-founder of Project Ploughshares, is an adjunct associate professor in peace studies at Conrad Grebel University College, and is a fellow of The Centre for International Governance Innovation in Waterloo.

The opinions expressed in this article/multimedia are those of the author(s) and do not necessarily reflect the views of CIGI or its Board of Directors.