In anticipation of today’s meeting of great powers in London to discuss Iran’s defiance of the U.N. Security Council, the Treasury Department is readying a new blacklist of companies and banks to be barred from American financial markets for their role in assisting the Islamic Republic’s nuclear program.

One Western diplomat who requested anonymity, said proposals started being shared between the Treasury Department and American allies last week, when a February 21 deadline for Iran to end uranium enrichment passed.

The diplomat said the Bush administration is seeking to expand the list of individuals and companies attached to U.N. Security Council resolution 1737, the sanctions passed unanimously on December 23. If the five permanent Security Council members meeting today in London will not go along with this measure, America will be prepared to draw up the new blacklist on its own, the source said.

Iran’s president increased the stakes before today’s meeting. In a national address carried on state-run radio yesterday, President Ahmadinejad said, “The train of the Iranian nation is without brakes and a rear gear. … We dismantled the rear gear and brakes of the train and threw them away sometime ago,” according to the Associated Press.

In response, Secretary of State Rice said on Fox News Channel, “They don’t need a reverse gear. They need a stop button.” Ms. Rice reiterated the American offer to enter direct talks with Iran as soon as the regime stops the enrichment of uranium.

Also yesterday, there were reports in the Iranian press of an Iranian satellite launch. The Associated Press quoted state-run television as saying the head of Iran’s Space Research Center, Mohsen Bahrami, announced a successful space launch. Communications and Information Technology Minister Mohammad Soleimani said yesterday that Iran would speed up its space program, AP quoted the official IRNA news agency as reporting.

The prospect of a nuclear Iran has worried President Bush, who has vowed repeatedly not to leave office without solving the problem, though he has also expressed a preference for a diplomatic solution.

One of the key policies that America and — more recently — Europe and Asian allies are pursuing is the waging of a financial war against the Iranians. On February 16, the Treasury Department added the Kalaye Electric Co., Kavoshyar Co., and Pioneer Energy Industries Co. to the Treasury blacklist. While the designation technically would allow the Treasury Department to seize the assets of the companies, the real effect of the designation is to heighten the financial risk for Western companies from which the Iranian banks and companies seek financial assistance. In January, the Treasury Department added the Sepah Bank, Iran’s fifth-largest bank, to the blacklist.

The other front for American action against Iran is in Iraq, where American soldiers have detained at least 36 Iranian nationals since December.

Speaking on CNN yesterday, Iraq’s national security adviser, Mowaffak al-Rubaie, said Iran has changed its tactics. “In the last few weeks, they have changed their position, and they stopped a lot of their tactics and a lot of intervention or interference in the Iraqi internal affairs,” he said.

An American intelligence analyst said he was not as hopeful. “At best, right now they are laying low,” he said of Iran’s Quds Force, which American commanders in Iraq have said is providing terrorists with roadside mines responsible for the most lethal attacks against American troops.