WASHINGTON — U.S. complaints about Russian compliance with the 1991 START nuclear arms control treaty had not been resolved when the pact expired last year, but the disputes never amounted to allegations of cheating, a senior administration official said Wednesday.

Rose Gottemoeller, chief U.S. negotiator of the newly completed follow-on START treaty, said in an interview that the most significant compliance issues were settled before negotiations began.

"We solved a whole load of problems in the last two years or so," she said.

Gottemoeller's remarks appeared designed to rebut opposition to the treaty in the Senate, where it has attracted strong criticism from some Republicans. The Senate Foreign Relations Committee had hoped to vote on the measure before its August recess, but there now is a chance the treaty won't get a Senate vote until after the November elections.

Gottemoeller is scheduled to testify on New START before the Senate Armed Services Committee on Thursday.

Meanwhile, seven former commanders of U.S. strategic nuclear forces endorsed the treaty in a letter to key senators Wednesday. Defense Secretary Robert Gates and Adm. Mike Mullen, chairman of the Joint Chiefs of Staff, also favor it.

In their letter, the former commanders said "there is little concern today about the probability of a Russian nuclear attack." The treaty, they wrote, sustains limits on Russian forces while allowing the U.S. to make needed reductions in its own forces.

President Barack Obama considers the pact a milestone for U.S.-Russian relations, but some Republicans in Congress have raised doubts about the treaty's value. Obama and Russian President Dmitry Medvedev signed the pact in April.

When disagreements over implementing the START treaty arose they were handled by a special U.S.-Russia dispute resolution commission. None ever rose to the status of an alleged violation, Gottemoeller said.

Of the compliance disputes that remained when the 1991 treaty expired, "these were minor issues that went away when START went out of force," she said, adding there were "some concerns that we had about them, some concerns that they had about us."

The most significant disputes, like movement of Russian SS-27 mobile missile launchers and U.S. inspection of re-entry vehicles aboard certain Russian missiles, were resolved, Gottemoeller said.

"We put our priority on resolving the main issues," she said.

Gottemoeller said neither side accused the other of violating provisions of START at any point.

Senate ratification of New START initially seemed certain, but Republicans, led by Sen. Jon Kyl, R-Ariz., have questioned whether the administration has committed sufficient resources to maintaining the remaining U.S. strategic nuclear arsenal — missiles aboard long-range bombers and submarines, and land-based missiles.

Also in question is whether New START constrains U.S. options for improving its missile defenses.

Another potential problem for the administration is the Senate's request for the written record of the yearlong negotiations between the U.S. and Russia. The administration has balked, saying that could limit its ability to maneuver in future negotiations.

The State Department on Wednesday released an unclassified version of a compliance report to Congress, the first such assessment of compliance on a range of arms control treaties since 2005.

Republicans had pressed for details on Russia's treaty compliance record.

Gottemoeller said the unresolved disputes cited in the new State Department report have no practical bearing on the New START treaty because all those disputes have been dropped. Nor should those disputes raise questions about Russia's reliable implementation of arms agreements, she said.

In releasing the report, State Department spokesman P.J. Crowley said that throughout the life of the 1991 START treaty, Russia was in compliance with the pacts' "central limits."

The released report is a condensed 95-page version of a classified, more detailed document submitted to Congress. The document said implementation of the 1991 treaty was successful, but added that "a number of long-standing compliance issues that were raised" in a U.S.-Russia dispute resolution commission remained unresolved when the treaty expired Dec. 5, 2009.

The report did not describe any of the unresolved issues. Gottemoeller said both sides had agreed to keep them confidential. She described the disputes as minor, technical matters.

The State Department report also said it was unclear whether Russia fulfilled its obligations as a signatory to the 1972 Biological Weapons Convention, which prohibits development, production and storage of biological agents or toxins of types not used for peaceful purposes.