As soon as next week, and after months of negotiations, Russia and the U.S. may sign a successor to the most extensive nuclear-weapons treaty before it expires December 5. National Security Adviser Jim Jones’ trip to Moscow late last month is what has fueled the diplomatic optimism—Jones offered a package of proposals called the Strategic Arms Reduction Treaty, or START, and the Russians reacted positively, if not formally. Russian President Dmitry Medvedev said Saturday that the two countries “have every chance” to sign a treaty by the year’s end. Nailing down a replacement for the expiring 1991 treaty is a key first step in President Obama’s arms-control agenda, and as the December deadline loomed, analysts had feared a lapse in the complex procedures that verify both sides conformed to the rules. The new START agreement will contain modest cuts in the number of deployed warheads each side is allowed. The new ceiling will be 1,500 to 1,675 city-annihilators for each nation, down from the 1,700 to 2,200 agreed to seven years ago.