MOSCOW  The Russian government has agreed to let American troops and weapons bound for Afghanistan fly over Russian territory, officials on both sides said Friday. The arrangement will provide an important new corridor for the United States military as it escalates efforts to win the eight-year war.

The agreement, to be announced when President Obama visits here on Monday and Tuesday, represents one of the most concrete achievements in the administration’s effort to ease relations with Russia after years of tension. But the two sides failed to make a trade deal or resolve differences over missile defense, and are struggling to draft a preliminary nuclear arms deal.

The blend of success and stalemate leading to Mr. Obama’s visit suggests that it is easier to talk about a “reset” button than to press it. The promise of a new era of cooperation was always predicated on the tenuous notion that a change of tone and a shift in emphasis might be enough to bridge deep divisions. But even with both sides eager for warmer ties, the issues that have torn Washington and Moscow apart did not go away with the transition at the White House.

Mr. Obama is less enthusiastic than President George W. Bush was about an antimissile system in Eastern Europe or NATO membership for Ukraine and Georgia, but has not abandoned either goal, to the consternation of the Kremlin. Despite American pressure, Moscow has not yielded in its confrontation with Georgia a year after their brief war.