Washington (CNN) -- The proposed U.S.-Russia Strategic Arms Reduction Treaty will enhance U.S. security and diplomatic credibility, and won't compromise U.S. nuclear force levels or undermine its missile defense, top U.S. officials said Tuesday as they urged the Senate to ratify the pact.
"We will strengthen our national security more broadly, including by creating greater leverage to tackle a core national security challenge, nuclear proliferation," said Secretary of State Hillary Clinton.
She joined Joint Chiefs Chairman Adm. Mike Mullen and Secretary of Defense Robert Gates in testifying before the Senate Foreign Relations Committee.
"The choice before us," Clinton said, "is between this treaty and no treaty governing our nuclear security relationship with Russia; between this treaty and no agreed verification mechanisms on Russia's strategic nuclear forces; between this treaty and no legal obligation for Russia to maintain its strategic nuclear forces below an agreed level."
Signed by U.S. President Barack Obama and Russian President Dmitry Medvedev on April 8, the treaty would cut the total number of nuclear weapons held by the United States and Russia by about a third. It would fix a ceiling for each country of 1,550 nuclear warheads and 700 deployed nuclear delivery vehicles.
The treaty will take effect only if ratified by lawmakers in both countries. In the United States, the Senate would have to approve the treaty by a two-thirds vote.
Gates said the treaty would foster transparency, predictability, strategic stability and access to Russian weapons and facilities.
Clinton, asked why the treaty should not be rejected, said it has built a "level of understanding" between Russia and the United States, most notably with respect to Iran. Clinton said the improved relationship helped the United States, Russia and other nations reach agreement on the latest U.N. draft resolution on Iran.
At the same time, the resetting of the U.S.-Russia relationship has not been good news for the nation's adversaries, she said.
If the treaty is rejected, she said, it would undermine U.S. leadership on the issue of nonproliferation.
Obama has called the treaty "the most comprehensive arms control agreement in nearly two decades." It builds on an agreement that expired in December.
But some top Senate Republicans have expressed skepticism about the accord.
Senate Minority Leader Mitch McConnell, R-Kentucky, said in a statement in April that the administration "will need to meet three requirements if it expects favorable consideration of the START follow-on treaty."
"The Senate will assess whether or not the agreement is verifiable, whether it reduces our nation's ability to defend itself and our allies from the threat of nuclear armed missiles, and whether or not this administration is committed to preserving our own nuclear triad," McConnell said.
Clinton said similar treaties have had support in Washington over the years. She said the 2002 Moscow treaty was approved by a vote of 95-0, and the 1991 START treaty was approved 93-6. She said President George W. Bush began the process that led to the new treaty more than two years ago.
"I am not suggesting that this treaty alone will convince Iran or North Korea to change their behavior, but it does demonstrate our leadership and strengthens our hand as we seek to hold these and other governments accountable, whether that means further isolating Iran and enforcing the rules against violators or convincing other countries to get a better handle on their own nuclear materials," Clinton said. "And it conveys to other nations that we are committed to real reduction and to holding up our end of the bargain under the nonproliferation treaty."