Russia Opens Route for U.S. to Fly Arms to Afghanistan By PETER BAKER MOSCOW — The Russian government has agreed to allow American troops and weapons bound for Afghanistan to fly over Russian territory, providing an important new corridor for the United States military as it escalates efforts to win the eight-year-old war, officials from both sides said Friday. The agreement, to be formally announced when President Obama visits here on Monday and Tuesday, represents one of the most concrete achievements of the effort to rebuild a relationship severely strained by last year’s war between Russia and Georgia. The new transit route will give American forces more alternatives as they encounter increasing trouble elsewhere. “Afghanistan is one of the areas where we must cooperate,” Mikhail Margelov, chairman of the foreign affairs committee in Russia’s upper house of Parliament, said in an interview. Russia understands, he said, that the United States and NATO forces in Afghanistan are effectively defending Russia’s southern flank. Until now, Russia has allowed only restricted use of its territory for the Afghan war, permitting shipments of nonlethal supplies by train. Under the new agreement, American officials said, military planes carrying lethal equipment as well as troops will be allowed to make thousands of flights a year through Russian airspace. As Mr. Obama prepared to leave Sunday for his first visit here since taking office, negotiators were trying to work out a preliminary agreement on nuclear arms cuts that he could announce along with President Dmitri A. Medvedev. But officials said they were still divided on important elements and not sure whether they would make a breakthrough in time. If successful, the two leaders hope to lay out a range of possible limits for warheads and delivery vehicles as well as address issues like the verification of conventional arms. The so-called framework agreement under discussion would lay out the parameters of a treaty to be drafted by the end of the year to replace the expiring cold war Strategic Arms Reduction Treaty. But Russia wants to tie the negotiations to the dispute over American plans to build a missile defense system in Eastern Europe. While Washington maintains the system is intended to defend against a future threat from Iran, Moscow sees it as aimed at itself and wants the agreement that Mr. Obama and Mr. Medvedev sign to link limits on offensive and defensive weapons. The agreement on Afghanistan was a high priority for Mr. Obama, who has ordered an additional 21,000 American troops to join the fight against the Taliban and Al Qaeda there. Supply routes through Pakistan have become complicated by that country’s increasing volatility, while Uzbekistan evicted American troops from a base a few years ago and Kyrgyzstan threatened recently to do the same. American negotiators recently persuaded Kyrgyzstan to change its mind by increasing payments for the base there.