WASHINGTON — The sweeping sanctions announced yesterday against Iranian banks and military institutions are dividing the Democratic Party’s field and drawing fire from the Russians, whose second largest oil company this week announced it would briefly suspend its development of an Iranian oil field.

Yesterday, Senator Clinton, the Democrat from New York who is leading in national polls for her party’s nomination as president, said she supported the terror designations in the action. But, she added, “I’ve been concerned for a long time over George Bush’s saber-rattling and belligerence toward Iran.”

The campaign of Mrs. Clinton’s chief rival for the nomination, Senator Obama, a Democrat of Illinois, fired back yesterday, calling Iran’s elite Quds Force a supporter of terrorist entities and dubbing Iran’s Revolutionary Guard a proliferator of weapons of mass destruction — a step on the road to war.

In a memo outlining the differences between his candidate and Mrs. Clinton, Mr. Obama’s chief foreign policy adviser, Greg Craig, said the New York senator’s vote on September 26 for a resolution recommending the designations created a new rationale for staying in Iraq by countering Iran’s influence with Shiite militias.

Democrats joining Mr. Obama in opposing the new sanctions were a former North Carolina senator, John Edwards, Senator Biden, and Senator Dodd. The chairman of the House Foreign Affairs Committee, however, Rep. Tom Lantos of California, issued a statement saying, “I hope this latest action signals that the Administration will now begin at last to place sanctions on foreign companies that invest in Iran’s energy sector, as required by law, and support expansion of those sanctions. Refusal to do so is simply inexplicable.”

The sanctions, which apply to Iran’s Revolutionary Guard and Quds Force as well as its Ministry of Defense, the Armed Forces Logistics Organization, and three major banks — Bank Melli, Bank Mellat, and Bank Saderat — may not apply to non-Iranian companies that do business with those entities as Mr. Lantos had wished.

At a press conference yesterday, Treasury Undersecretary Stuart Levey said, “We’re not threatening secondary sanctions on institutions. What I think Secretary Paulson is trying to say, and what I’m trying to express as well, is that financial institutions are making these decisions on their own, and that’s — we think — a positive development.”

Since 1997, the president and secretary of state have had the option to bar banks and companies that do business with Iran’s energy sector from American financial markets. Neither President Bush nor President Clinton has ever applied such a sanction. Mr. Levey has been successful in persuading European and Japanese banks though to cut ties with Iran voluntarily.

Secretary of State Rice yesterday said the decision to announce the new financial sanctions was due in part to Iran’s unwillingness to take her up on an offer she made on June 1, 2006, to negotiate directly over Iran’s nuclear program. Iranian facilities in Natanz have been spinning uranium centrifuges, in violation of an agreement made in 2003 with United Nations, for nearly two years. “Unfortunately, the Iranian government continues to spurn our offer of open negotiations, instead threatening peace and security,” Ms. Rice said.

Initially, Ms. Rice had held off announcing the new sanctions while her diplomats ironed out a third U.N. Security Council resolution censuring Iran for its continued enrichment activities. Yesterday, President Putin of Russia, whose country has a veto at the U.N. Security Council, said the move would force Iran into a corner.

“Why should we make the situation worse, corner it, threatening new sanctions?” Mr. Putin told reporters in Lisbon. “Running around like a mad man with a blade in one’s hand is not the best way to solve such problems.”

The chief of Iran’s Revolutionary Guard, General Ali Jafari, said that despite the new sanctions, the guard would be “ready to defend the ideals of the revolution more than ever before.”

Iran’s Revolutionary Guard is not only the largest component of Iran’s military, but it is increasingly the master of Iran’s economy, according to western analysts. The guard today controls contracts to develop much of the country’s oil and gas sector.

The designation of the elite Quds Force, a component of the guard, may also have implications for the war in Afghanistan. When the proposal for the sanctions was initially approved in early summer by the National Security Council, lawyers for the Pentagon’s Central Command, which encompasses the wars in Iraq and Afghanistan, wrote memos to the National Security Council asking whether the designation would effectively change the rules of engagement, allowing soldiers to target members of the Quds Force in Afghanistan. Since last December, the Iraq military has waged a war there against Iran’s Quds Force. The Pentagon in the last three months has accused the Quds Force of arming Taliban rebels in Afghanistan.

An administration official yesterday said it was still an open question inside the administration. “Nobody is saying we are going into Iran, but it raises important questions about what is and is not possible,” the official said.