Washington (CNN) -- Secretary of State Hillary Clinton urged Senate ratification of the new nuclear arms treaty with Russia on Wednesday, stressing that it's a critical component of U.S. efforts to keep tabs on Moscow's arsenal.
"It will advance our national security and provide predictability and stability" between the world's top two nuclear powers, she told reporters at the State Department.
There is nothing in the measure that will prevent the United States from modernizing its arsenal and maintaining a "safe, secure and effective" deterrent, she said.
The Strategic Arms Reduction Treaty, signed in April by President Barack Obama and Russian President Dmitry Medvedev, cuts the total number of nuclear weapons held by the United States and Russia by about a third. Specifically, it fixes a ceiling for each country of 1,550 nuclear warheads and 700 deployed nuclear delivery vehicles.
"Opposing ratification means opposing the inspections [that] provide us a vital window" into Russia's nuclear arsenal, Clinton warned. "As time passes, uncertainty will increase," leading to greater unpredictability.
The last START treaty expired in December.
Some top Senate Republicans have expressed skepticism about the accord, arguing among other things that it complicates U.S. efforts at developing a missile defense system.
Clinton, Defense Secretary Robert Gates and Adm. Michael Mullen, chairman of the Joint Chiefs of Staff, testified before the Senate Armed Services Committee in June that the treaty will not constrain U.S. efforts to develop a shield against ballistic missiles coming from rogue states like Iran and North Korea.
The United States abandoned the Nixon-era Anti-Ballistic Missile treaty under the Bush administration in 2001 and has been experimenting with missile defense systems extensively since then. While tests of short-range and sea-based systems have been largely effective, longer-range systems aimed at protecting the U.S. homeland have a mixed record of success.
The Obama administration scrapped the Bush administration's plan for a European-based missile defense system in Poland and the Czech Republic, proposing instead a more limited system aimed at defending against possible attacks. Both proposals have drawn opposition from Russia.
The Senate Foreign Relations Committee is set to begin formal consideration of the new treaty in mid-September, Clinton noted. She urged the chamber's Republicans to extend what she characterized as a long track record of bipartisan support for nuclear arms agreements.
The treaty needs 67 votes in the Senate to be ratified. The Russian parliament is not expected to approve the accord until the Senate ratifies it.
CNN's Elise Labott and Maxim Tkachenko contributed to this report