President Barack Obama and President Dmitri A. Medvedev of Russia moved closer to agreement Saturday on a long-stalled arms control treaty that would slash the Active nuclear arsenals of both countries by more than one-quarter, officials from both countries said. Obama and Medvedev spoke for 30 minutes by telephone to try to resolve remaining differences and set the stage for an accord before a nuclear summit meeting in Washington next month. In a statement, the Kremlin suggested that the two sides were ready to plan a signing ceremony for the treaty, which would replace the expired Strategic Arms Reduction Treaty of 1991, or START. 'It is now possible to talk about specific dates for the submission of the draft START treaty for signing by the heads of state,' the Kremlin statement said. The White House was more cautious, with its spokesman, Mike Hammer, saying the leaders 'had a good conversation' about 'the progress and consensus reached' in Geneva negotiations. 'The results of their talks are encouraging, and both leaders are committed to concluding an agreement soon,' Hammer added. Other administration officials, who insisted on anonymity to discuss delicate negotiations, said the call was initiated by Medvedev to confirm agreement on a set of issues in the treaty reached by negotiators in Geneva in recent days. They said the two sides must now hash out technical issues related to monitoring and verification, but they sounded more optimistic than they have in weeks. The two countries have been haggling over the new treaty for nearly a year and missed their self-imposed deadline of finishing by the time the original Start accord expired in December. While most of the substance has been settled for months, missile defense and verification have proved hard to resolve. 