Negotiators worked intensively for weeks to try to complete a legally binding "bridging mechanism," which would be in force until the two countries finalize and ratify a follow-on to the Strategic Arms Reduction Treaty (START I), which expired at midnight Friday. Still, they were unable to meet the deadline.

"Recognizing our mutual determination to support strategic stability between the United States of America and the Russian Federation, we express our commitment, as a matter of principle, to continue to work together in the spirit of the START treaty following its expiration, as well as our firm intention to ensure that a new treaty on strategic arms enter into force at the earliest possible date," the White House said in a brief statement.

However, "in the spirit" does not mean that START will continue to be legally binding, Obama administration officials said, and some verification procedures that were required by the pact will be discontinued.

The Washington Times first reported this week that the administration signed an agreement in October to end full-time U.S. inspections at Russia's only long-range missile facility. An expert team has counted every missile leaving the assembly line for 15 years.

State Department officials expressed hope that a new treaty would be negotiated by month's end, though ratification by the two countries' legislatures is expected to take much longer.

Daryl Kimball, executive director of the Arms Control Association, said the White House announcement was a "bridging statement that recognizes the value of START." He added that the "bridging mechanism" and the follow-on pact would most likely be completed at the same time.

"The world doesn't end on Dec. 5," he said in reference to START's expiration.

However, Republican members of Congress were displeased with the administration's failure to secure a temporary deal.

Sen. Richard G. Lugar of Indiana, ranking Republican on the Senate Foreign Relations Committee, sponsored legislation last month to keep certain verification measures in place until a new treaty is completed. The administration, however, said that legislative action was not necessary and a transition document would be prepared by the executive branch.

One of the procedures Mr. Lugar's bill would have preserved is having on-site inspections at the Votkinsk Machine Building Plant, about 600 miles east of Moscow — the site where all Russian intercontinental ballistic missiles (ICBMs) are built.

Although officials on Capitol Hill said they were not informed of the decision, the administration has given up access to Votkinsk.

"U.S. and Russian officials signed on Oct. 20 a series of documents, which establish the procedures to be followed for the completion of U.S. monitoring activities at the Russian ICBM production facility at Votkinsk," a State Department official said.

Congressional officials said they were told by the Obama administration that it "got stuck" with a deal made by the George W. Bush administration to close the monitoring facility at Votkinsk.

Paula A. DeSutter, assistant secretary of state for verification, compliance and implementation in the Bush administration, said she sent the Russians a post-START proposal in November 2008, but it was not a negotiated agreement and the Obama team could have changed it.

A Republican Senate aide said the current administration started negotiations on a "bridging mechanism" too late. "Why didn't they do that weeks ago?" he asked, speaking on the condition of anonymity because of the sensitivity of the topic.

Mr. Kimball said the White House did not have enough time. He blamed the Bush administration for not having started negotiations with Russia during its term, which he said would have given the Obama administration a head start.

Republicans, in turn, said that would not have been prudent because of the two administrations' different approaches to arms control, with the Obama administration seeking deeper cuts in nuclear arms.

During a visit to Moscow by President Obama in July, both countries agreed to draft a new arms control treaty that would replace START. They also set a goal of cutting the number of strategic nuclear warheads to between 1,500 and 1,675 within seven years. Currently, the U.S. deploys about 2,200 such warheads and Russia is estimated to have between 2,500 and 2,600.