"The military option is at the end of the day, and still only a temporary option," he said.
Gates told Senate appropriators Thursday that a military attack on Iran would merely send that country's nuclear program further underground. Instead, he said that the United States and its allies must convince Tehran that its nuclear ambitions will spark an arms race that will leave the country less secure.
"All of the information we get indicates that however imperfect the UN resolutions against Iran are, the Iranians hate it when one of those resolutions passes, because it makes clear how isolated they are in the world.
"My view is that it's the only way to eliminate an Iranian determination to have nuclear weapons…even a military attack will only buy us time and send the program deeper and more covert," he said. Gates added that the price of oil was also a factor in the success of a diplomatic effort to curb Iran's nuclear program.
"I would tell you we've got a better chance of making it work on $40 oil than we do on $140 oil," he said.
Gates and Secretary of State Hillary Rodham Clinton said the US should work with its allies on tougher international sanctions. Gates also said that the US should pursue partnerships with Russia on missile defense programs in the region to further isolate Iran and to give Tehran economic and diplomatic reasons to voluntarily abandon its nuclear interests.
"It's one of the reasons I think there is value in pursuing a partnership with the Russians on missile defense in Europe and in Russia itself," he said.