WASHINGTON — In private talks with foreign bankers, U.S. officials are highlighting the risks of operating in Iran in a bid to squeeze the country's hard-line clerical regime.

The campaign, which has yet to seriously pinch the Iranian economy, is intended to impress upon Tehran the costs of its controversial nuclear program.

"You're starting to see financial institutions looking at what's happening in Iran, the things their president is saying, the activities they're engaged in ... the nuclear program and state sponsorship of terrorism and making their own decisions," says Stuart Levey, undersecretary of the Treasury for terrorism and financial intelligence.

Last month, the Organisation for Economic Co-operation and Development downgraded Iran as a credit risk, raising insurance premiums on Iranian export credits.

In January, UBS and Credit Suisse separately announced they were halting operations in Iran. Both said they acted after internal assessments, rather than because of Bush administration pressure.

ABN Amro's Sierk Nawijn would not directly address the role U.S. pressure may have played in the Dutch bank's approach, saying only: "We comply with all applicable laws and regulations."

In December, ABN Amro was fined $80 million after its Dubai branch was found to have breached U.S. money-laundering regulations on transactions involving Iran and Libya.

The U.S. has maintained a near-total financial embargo on Iran since 1995. Banks with U.S. operations — governed by U.S. law — are allowed to process payments for trade between Iran and third countries. But they must certify that the goods being traded are themselves not prohibited.

Over the past six months, more aggressive U.S. enforcement of this restriction has coincided with several European banks curtailing their involvement in Iran.

"The U.S. is now implementing the 1995 law a lot more and putting pressure on international banks," says Siamak Namazi, a Tehran-based consultant.

Given a choice between their modest Iranian business and antagonizing the U.S. government, some banks require little persuading. The Iranian government has a reputation for being indifferent, at best, to foreign investment.

"There's quite an effort being made by several governments, not just the U.S. government, to convince heads of companies," says Patrick Clawson of the Washington Institute for Near East Policy.

Small-business owners in Iran will find bank letters of credit for their international trading more costly. In April, Levey told a Senate committee that banks abandoning Iran could have "tremendous impact."

But it's not clear that the oil-rich Iranian economy can be badly damaged this way. Earlier U.S. sanctions also have been imperfect: American goods shipped via third countries such as Dubai are a common sight in Iranian markets.