The Kremlin released the statement Friday saying Russian President Dmitry Medvedev and President Obama pledge to continue to work together "in the spirit" of the expiring 1991 Strategic Arms Reduction Treaty. The White House says it had planned to issue a similar statement Saturday.
Meanwhile, U.S. and Russian negotiators are working intensively to reach a deal for a successor to the treaty that expires at 7 p.m. EST Friday.
The pledge appears to mean that the two sides will continue to respect the expiring limits on arms and to allow inspectors to verify they are living up to the deal.
The expiring START treaty, signed by Soviet President Mikhail Gorbachev and President George H.W. Bush in 1991, required each country to cut its nuclear warheads by at least one-fourth, to about 6,000, and to implement procedures for verifying that each side was sticking to the agreement.
The legal basis for the procedures, including inspections of nuclear facilities, also will expire Friday. Both sides are expected to allow each other to continue them until a new deal is in place.
The State Department said this week that it believes the two sides can keep some of the verification procedures in place through an informal political agreement that is not legally binding.
Meanwhile, negotiators still are grappling over verification procedures for the new treaty, which have become the final sticking point preventing a deal.
The Obama administration would welcome a quick conclusion to demonstrate an improvement in U.S.-Russian relations and to gain momentum for other arms control and nonproliferation goals. Washington also is looking for cooperation on issues including reining in Iran's nuclear ambitions. However, Russia has fewer incentives for an immediate deal.
Obama and Medvedev agreed at a Moscow summit in July to cut the number of nuclear warheads each possesses to between 1,500 and 1,675 within seven years as part of a broad new treaty.
The Obama administration also had held out hope that a deal could be sealed in time for Obama's trip to Europe to accept the Nobel Peace Prize on Dec. 10. It appears unlikely, however, that a breakthrough will happen by then.
The Associated Press contributed to this report.