As the Bush administration struggles to rally international pressure on Iran to halt its nuclear program, China and Russia are working to take the most powerful diplomatic weapon off the table: the military option.

Moscow and Beijing insist that a U.N. sanctions resolution under negotiation in New York should avoid language that could be used as a pretext for a military strike against Iran's nuclear facilities. They have received the tacit backing of the United States' key European partners, Britain, France and Germany.

But analysts say the 15-nation Security Council's refusal to preserve the possibility -- however remote -- of military action has weakened its hand as it confronts one of the most significant challenges of the 21st century: the possible emergence of a radical Middle East government with nuclear weapons.

"What means of enforcement is credible if you start out by saying in the beginning that 'oh, by the way, we're not going to do the one thing that you're most afraid of?' " said Patrick Clawson, deputy director for research at the Washington Institute for Near East Policy. He said the council should "have the military option on the table" in the event that the government that threatened to wipe Israel off the map does develop nuclear weapons.

The effort to constrain the United States underscores lingering distrust over the Bush administration's decision to invade Iraq in March 2003 without explicit Security Council approval, analysts said. It follows a similar push to prevent the United States from adopting U.N. resolutions that one day may be used to punish Sudan and North Korea with stronger sanctions or military force.

"People are afraid it's a slippery slope; that if they agree to sanctions today, they give the authority for military intervention tomorrow," said Edward C. Luck, a Columbia University historian who studies the United Nations. He said the political dispute over the use of force has eroded the council's credibility. "It is a sign of weakness and division," Luck said.

The U.N. debate over the use of force in Iran coincides with a realignment of power in the region that is already diminishing the prospects for U.S. military action against Iran, analysts say. U.S. and NATO military setbacks in Iraq and Afghanistan are eroding public support in the United States for military action in the region. And the United States' European allies are firmly opposed to any U.S. military action in Iran.

The Bush administration maintains that though it never takes the military option off the table, its diplomatic campaign to rally support for sanctions against Iran and North Korea is not a cover for launching new conflicts.

But Russian and Chinese diplomats note that the United States insisted it was committed to diplomacy in the months leading up to the March 2003 invasion of Iraq. When the United States and Britain failed to secure U.N. backing for a more forceful response, they turned to a 12-year-old resolution as the legal basis for the invasion. Resolution 687 set out the terms of a cease-fire ending the 1991 Persian Gulf War.

"We learned our lesson from what happened in Iraq and that's why we want to be very clear," said a Chinese diplomat, who spoke on the condition of anonymity.

Russian Foreign Minister Sergey Lavrov, Moscow's former ambassador to the United Nations, told reporters in March that the debate over Iran reminded him of the run-up to the U.S.-led invasion. "That looks so deja vu," Lavrov said. "I don't believe that we should engage in something which might become a self-fulfilling prophecy. We are convinced that there is no military solution to this crisis."

But some U.N. observers fear the feud has undercut the body's ability to bluff, emboldening Iran, North Korea and Sudan to openly defy the Security Council and get away with it. "There's a sort of almost tin hollow quality to some of its pronouncements," U.N. Deputy Secretary General Mark Malloch Brown said of the Security Council in a speech last month at the Brookings Institution.

Malloch Brown suggested that Sudan's President Omar Hassan al-Bashir has interpreted the council's inaction as a sign of weakness, and rebuffed its demand to allow more than 20,000 U.N. peacekeepers into Darfur, Sudan, to bring an end to one of the worst human rights calamities in Africa in a decade.

"President Bashir looks at us and he thinks he's seen us blink, and that makes it hugely difficult to credibly address this issue of winning his consent to our deployment," Malloch Brown said. Though he acknowledged there is no stomach for using force to compel Bashir to accept U.N. forces, he said "we can never take the military option off the table."

The U.N. debate over the use of force in Iran and North Korea has focused on Chapter 7 of the U.N. Charter, a provision that has traditionally been used to enforce U.N. demands through the threat of economic sanctions or military action. Russia and China have refused to support the provision, arguing that it could be used to justify future military action.

The Bush administration argues that a Chapter 7 resolution is required to make sanctions compulsory. "It is simply incorrect" that the phrase "somehow authorizes the use of force," John R. Bolton, the U.S. ambassador to the United Nations, said last month.

"There is a suspicion, a misperception that this leads inexorably to the use of force, and it doesn't," British Ambassador Emyr Jones Parry added during recent negotiations on North Korea.

Britain, France and Germany brokered a compromise sanctions resolution on Iran that cites Chapter 7, but it explicitly rules out the possibility that it could be used as a pretext for military action.

Some U.N. experts say the debate exaggerates the importance of a Chapter 7 provision in authorizing the use of force. They note that Chapter 7 was never invoked to authorize the United Nations' two most important Cold War enforcement operations, the Korean War and the 1960 Congo peacekeeping operation. The U.N. Security Council did not cite Chapter 7 when it granted U.N. peacekeepers the right to use force against Israeli troops or Hezbollah militia to enforce a cease-fire between the two combatants.

It may be harder to justify military action without using Chapter 7, "but it doesn't completely shut the door," said Colin Keating, New Zealand's former ambassador to the United Nations and the director of the New York-based Security Council Report.