WASHINGTON » The Obama administration is working on a series of sanctions that would take aim at the Islamic Revolutionary Guards Corps of Iran, publicly singling out the organization's vast array of companies, banks and other entities in an effort to curb Tehran's nuclear ambitions.

Senior White House officials described what they said would be a “;systematic”; effort to drive a wedge between the Iranian population and the Revolutionary Guards, which the West says is responsible for running Iran's nuclear program and has a record of supporting militant Islamist organizations and cracking down on anti-government protesters.

In formulating a U.N. Security Council resolution that names specific companies and the wide web of assets owned by the Guards, which include even the Tehran airport, the administration is hoping to substantially increase pressure on the organization, which one senior administration official described as a new “;entitled class”; in Iran.

“;We have bent over backwards to say to the Islamic Republic of Iran that we are willing to have a constructive conversation about how they can align themselves with international norms and rules and re-enter as full members of the international community,”; President Barack Obama said in a news conference on Tuesday. “;They have made their choice so far.”;

The United States, Obama said, will be working on “;developing a significant regime of sanctions that will indicate to them how isolated they are from the international community as a whole.”;

The goal would be to increase the cost for those who do business with Iran so much that they would cut off ties.

Previous resolutions have designated a handful of senior figures in the Iranian nuclear program, including the man believed to run much of the military research program for the Revolutionary Guards. But the administration's latest push would name dozens, if not hundreds, of companies.

By all accounts, the sanctions will be powerful only if the United States can get the support of Russia and China, which do extensive business with Iran and the Guards. The Americans said that they believed that they would have the support of Russia, but it remains uncertain whether China will go along. Administration officials are still working to convince Beijing that it is in China's own national security interests to act against Iran. Russia and China are two of Iran's major trading partners.

The divergent reactions to Iran's announcement on Tuesday that it had begun enriching uranium to a higher level signaled the coming hurdles for the administration. While Russia, the United States and Europe all reacted sharply, news reports on Tuesday quoted a Chinese Foreign Ministry spokesman, Ma Zhaoxu, as urging continued “;dialogue and negotiations.”;

Prime Minister Benjamin Netanyahu of Israel told European diplomats that Iran was “;racing forward to produce a nuclear weapon,”; Reuters reported. “;This means not moderate sanctions, or watered-down sanctions,”; he said. “;This means crippling sanctions and these sanctions must be applied right now.”;

Iran, which contends that its nuclear program is for civilian purposes, says that it is enriching uranium to 20 percent purity to fuel a medical reactor, not the 90 percent level required for a nuclear weapon. While it remains unclear whether Iran has the ability to do either, the West contends that the program's goal is to produce nuclear weapons.

Defense Secretary Robert M. Gates called for a new Security Council resolution within “;weeks,”; and other administration officials said they would like to see a resolution passed by the end of March.

While sanctions against the Revolutionary Guards are at the core of the proposals the United States is circulating, administration officials and European diplomats said they hoped that the package would include other elements as well, including an expanded list of Iranian officials who are denied visas to visit the West and the curbing of investments in Iran's energy sector.

Last week in London, Secretary of State Hillary Rodham Clinton laid out the American arguments to the Chinese foreign minister, Yang Jiechi. Administration officials are trying to convince China that a nuclear-armed Iran would so disrupt the Persian Gulf that it would pose a far greater threat than any potential rupture in China's commercial relations with Iran. Among the threats is that Israel would preemptively bomb Iran's nuclear facilities.

“;If you're China, you do a simple cost-benefit analysis on the impact on oil prices,”; said Karim Sadjadpour, an Iran expert at the Carnegie Endowment for International Peace. “;With an Israeli strike, oil prices would skyrocket.”;

Whether that argument convinces China remains to be seen; administration officials were unwilling to make predictions when asked if they believed that they had Beijing's support.

So the wooing of China continues, with the United States also trying to line up Persian Gulf countries, like Saudi Arabia and the United Arab Emirates, to reassure China that they would offset any cutoff in oil shipments that could result from its support of sanctions.

Clinton, who is traveling to Qatar and Saudi Arabia this weekend, is expected to raise this issue, officials said.

Senior officials point to their successful effort to win Russia's backing for tougher sanctions as a model of how they might convince China. Obama put the subject at the top of his agenda in talks with the Russian president, Dmitri A. Medvedev, something he is now doing with the top Chinese leadership.

Analysts warn, however, that the Russia analogy can be taken only so far. China has much broader commercial ties with Iran, including multibillion-dollar investments in its oil and gas sector.

Some analysts also point to a recent stream of tough statements from Beijing—on issues like currency policy and the Dalai Lama—as evidence that China is flexing its muscles on the global stage. It is no longer clear, they said, that Beijing will reflexively follow Moscow in its backing of Iran sanctions.

As the Obama administration lays the groundwork for a resolution, it is racing against a couple of timetables.

The first is set by Iran's nuclear program and the administration's sense of urgency to act. The second is set by the dynamics of the Security Council, where France currently presides.

The French president, Nicolas Sarkozy, has been aggressive in pushing for new sanctions, especially in the energy sector, according to U.S. and European officials. The next member to hold the chairmanship of the Security Council is Gabon, an African nation less likely to push hard for a resolution.