The measure, which would give the president powers to take action against foreign companies that sell refined petroleum to Iran, is popular on Capitol Hill, and three-quarters of House members have co-sponsored the legislation. But the measure could undermine Obama administration efforts to negotiate with Iran over its nuclear development program. If talks fail and further sanctions become necessary, administration officials would rather enact measures supported by many countries. 'We prefer this be done in a multilateral fashion,' said Ian Kelly, a State Department spokesman. The legislative measure still must win passage by the full House and Senate. But initial approval by the House Foreign Affairs Committee came at an important moment. The Iranian leadership is expected to announce Thursday whether it accepts an international proposal to modify its existing stocks of enriched uranium for medical and research purposes. If Iran accepts, the deal could delay what the West suspects is a push to develop nuclear weapons. Western governments hope acceptance would open the way to further agreements on the nuclear program, which Iran says is for civilian purposes only. Rep. Howard Berman, D-Calif., chairman of the Foreign Affairs Committee, said the bill will 'at least, force the Iranians to think twice about continuing to flout the will of the international community.' Even though Iran is a leading crude oil producer, it must import 40 percent of its gasoline, a point of economic vulnerability. Mark Dubowitz, executive director of the Foundation for the Defense of Democracies, said that the harsh measures 'may not be the silver bullet that ends the regime's illegal nuclear weapons program, but they can be silver shrapnel which can severely wound the regime.' Advocates contend that Iran has been stringing the West along on efforts to secure a nuclear deal. Tough economic measures, they believe, will force the Iranian public and leadership to decide whether the nuclear program is worth the hardship and international isolation. Critics contend that the measures would punish average Iranians without affecting the leadership. They say that sanctions also could disrupt Western unity by pressuring European companies to give up their sales to Iran, opening the way for China and Persian Gulf states to provide much, if not all, of the supply. The bill also would allow the president to go after companies that provide ships to transport the fuel or that underwrite or finance the cargo. Even so, some analysts are skeptical about the persuasive power of such steps with the Iranians, who have ignored a series of punishments from the United Nations and various countries acting on their own. 'Iran is a risk-acceptant country that believes the wind is still very much at its back,' said Cliff Kupchan, a former congressional aide now at the Eurasia Group, a private analysis company. 'There's reason to be skeptical that this would change Iranian policy.' 