For years, American intelligence officials have objected to publishing quantitative descriptions of the American nuclear arsenal, concerned that the figures might help terrorist groups calculate the minimum nuclear fuel needed for a weapon. But administration officials said reputable Web sites that track such issues have long noted that American weapons designers need an average of around 4 kilograms of plutonium, or 8.8 pounds.

“It became clear there was a way to get the transparency without revealing any state secrets,” a senior administration official said, declining to speak on the record because the numbers had not yet been declassified.

The numbers will combine three categories of weapons: deployed, in “active reserve” and in inactive storage. They exclude weapons designated for decommissioning. The United States and Russia have already revealed the number of deployed strategic weapons they possess. Britain and France have recently revealed details of their stockpiles. China has said little. India, Pakistan and Israel — which have all refused to sign the treaty — have not revealed numbers.

http://www.nytimes.com/2010/05/03/world/03weapons.html