Leaders of a bipartisan House panel, seeking economic pressure against Iran, moved Thursday to reduce Tehran's import of gasoline.

A bill introduced by Reps. Mark S. Kirk, R-Ill., and Robert E. Andrews, D-N.J., who set up a congressional working group on Iran's nuclear programs two years ago, coincided with angry protests in Tehran against fuel rationing.

While Iran is one of the world's largest oil producers, a lack of refineries compels it to import nearly half the gasoline used by Iranians.

Besides the rationing, which sparked street demonstrations in Tehran and criticism of Iranian President Mahmoud Ahmadinejad, the government boosted gasoline prices last month.

Under the proposed congressional legislation, any company that provides Iran with gasoline or helps it import gasoline after the end of the year could lose its access to American customers through sanctions.

"This is becoming the critical weakness of the Iranian government, meaning its dependence on gasoline," Kirk said in a telephone interview. "The riots show the gasoline shortage is a growing danger to the Iranian regime and a diplomatic opportunity for Western countries to force Iran to adhere to international nuclear rules."

Most of Iran's gasoline imports come from Persian Gulf states and India, brokered by the Dutch trading house Vitol. Most of the gasoline tankers are insured by Lloyds of London.

On Tuesday, the House Foreign Affairs Committee approved legislation designed to strike at investments in Iran.

That bill, championed by the committee chairman, Rep. Tom Lantos, D-Calif., would end the Bush administration's power to waive sanctions against foreign companies that invest in Iran.

"Our goal must be zero foreign investment," Lantos said.

A State Department spokesman, Tom Casey, agreed Thursday that "we need to do everything that we can to continue to raise the stakes in Iran in terms of its nuclear program."

He said the United States was working with friends and allies in Europe and elsewhere to gradually ratchet up sanctions against Iran.

"We are in the process now of looking at what additional measures we can add," Casey said.

However, the spokesman also said the administration had to move carefully in order to hold together "the broad international coalition that we've worked to build."

Several countries that do lucrative business with Iran have balked at applying severe pressure on the Tehran government.

Among the arguments the Bush administration has with Iran is its nuclear program. The United States and its European allies are convinced that Tehran is trying to build nuclear weapons. Iran insists its program is aimed at developing civilian energy.