Washington (CNN) -- The Obama administration pushed for Senate approval of the new nuclear arms treaty with Russia on Thursday, hoping to win over Republican lawmakers concerned the pact imposes limits on U.S. missile defense programs.
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.
Some top Senate Republicans, however, have expressed skepticism about the accord, arguing it ties the U.S. hand in developing a missile defense system.
Secretary of State Hillary Clinton, Defense Secretary Robert Gates and Adm. Michael Mullen, chairman of the Joint Chiefs of Staff, told the Senate Armed Services Committee that the START treaty did not constrain U.S. efforts to develop a shield against ballistic missiles coming from rogue states like Iran and North Korea.
Moscow has said it reserves the right to withdraw from the treaty if Washington develops a missile shield -- "But that is not an agreed-upon view," Clinton said.
"That is not in the treaty. It's the equivalent of a press release, and we are not in any way bound by it," she said.
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 based in Poland and the Czech Republic, proposing instead a more limited system aimed at defending against possible attacks from rogue states like Iran. Both proposals have drawn opposition from Russia.
But Clinton said "The United States intends, and in fact is continuing, to improve and deploy effective missile defense systems." And she gave a categorical no when asked if there were any secret or side deals with Russia that prevented the Washington from moving ahead with missile defense.
Gates added there is nothing in the treaty or in U.S. statements "in any way, shape or form that would impose any limits on our plans to develop a missile shield." Gates and Energy Secretary Stephen Chu, who was also at the hearing, further argued that the treaty would provide the United States a needed opportunity to modernize its aging nuclear stockpile to make safer, more secure and more reliable weapons.
"I see this treaty as a vehicle to getting what we need in the way of modernization," Gates said. And Clinton said the pact would strengthen the U.S. hand to prevent the spread of illicit nuclear materials.
The treaty needs 67 votes in the Senate to be ratified. Russia's parliament has not yet ratified the pact.