NATO allies traded blunt words over Iraq today, with Defense Secretary Donald H. Rumsfeld saying that opposition to war was undermining the alliance, and French and German officials criticizing the U.S. approach as risky.

Rumsfeld told a largely European audience at a conference on international security that "diplomacy has been exhausted, almost." "A large number of nations have already said they will be with us in a coalition of the willing, and more are stepping up each day. . . . Clearly, momentum is building," he said.

Rumsfeld also warned that the United Nations is on "a path of ridicule" and that NATO could be in danger of heading the same way. He said France and Germany face diplomatic isolation with their opposition to an attack on Iraq.

German Foreign Minister Joschka Fischer, whose speech immediately followed Rumsfeld's, seemed taken aback by the relentlessness of the U.S. defense secretary's criticism. On the question of attacking Iraq, Fischer asked several times: "Why now? . . . Are we in a situation where we should resort to violence now?"

At one point Fischer faced the U.S. delegation to the conference and, switching from German to English, pointedly said, "Excuse me, I am not convinced."

Fischer also warned the United States against biting off more than it can chew in Afghanistan and the Middle East. "You're going to have to occupy Iraq for years and years," he said. "Are Americans ready for this?" If the U.S. public balks at the costs of a long-term military presence in Iraq, he said, then the U.S. military might withdraw from Iraq prematurely, further destabilizing the Middle East.

The French defense minister, Michele Alliot-Marie, joined the counterattack, raising her eyebrows at the "combative tone" of Rumsfeld's comments. "Ad hoc coalitions" are a precarious approach that can't replace the alliance, she cautioned.

The day exposed extraordinary tension between the United States and two of its main European allies, and also among European officials themselves. While all sides condemned the Iraqi leader, Saddam Hussein, they clashed repeatedly on how to deal with him.

A few blocks from the conference site, thousands of German antiwar demonstrators gathered despite a heavy snowstorm in support of their government's position. With hundreds of police officers nearby, the protesters rallied in a square in downtown Munich under signs such as "Remember Vietnam," "Christian Bombs for Muslim Oil" and "Rummy Go Home."

Another banner said, "Welcome to Cuba," an allusion to Rumsfeld's remark at a congressional hearing last week that the only nations determined not to help the U.S. attack Iraq are Cuba, Germany and Libya.

The rhetoric inside the conference was almost as heated. At one point, Portuguese Defense Minister Paulo Portas reminded Fischer of the failures of European pacifism, beginning with its inability to counter the rise of Nazism in the 1930s. Fischer responded brusquely, "You don't need to talk to me about that" and noted that he had supported the use of force in the Serbian province of Kosovo and in Afghanistan.

But the biggest divide was between the United States and the Europeans. Sen. John McCain (R-Ariz.) said that "Iraq is the test" of both the U.N. and NATO. He charged that the alliance is failing the test because of the "flawed calculations" and "vacuous posturing" of Germany and France.

McCain and Rumsfeld both said that recent French and German foot-dragging over even discussing the possible deployment of NATO assets, such as Patriot anti-missile batteries, to Turkey also threatened to damage the alliance.

But it was Rumsfeld's vintage performance, which focused almost entirely on Iraq and the consequences of positions being taken by various nations on how to deal with it, that set the tone for the day.

Rumsfeld emphasized that war with Iraq is "the last choice" but essentially argued that it is the only choice left. Diplomacy and economic sanctions have been "tried extensively" and failed to lead to Iraq's disarmament, he said.

Asked if he thought Germany and France were simply trying to check the unrestrained exercise of power by the United States, Rumsfeld responded that if that were so, "the likely effect would be that Germany and France would isolate themselves."

Rumsfeld also slammed the United Nations for recently making Libya the chair of a human rights commission and giving a similar position on a disarmament panel to Iraq. "That these acts of irresponsibility could happen now, at this moment of history, is breathtaking," he said. Rumsfeld called on the United Nations to move "from a path of ridicule to a path of responsibility."

If the United Nations doesn't change course, it runs the danger of repeating the failure of its predecessor, the League of Nations, Rumsfeld warned. "When the League failed to act after the invasion of Abyssinia [by Italy in 1935], it was discredited as an instrument of peace and security."

NATO Secretary General George Robertson sought to tone down the rhetoric, saying that strains in the alliance come and go. But he also conceded that it is part of his job to minimize cross-Atlantic tensions. "As secretary general of NATO, I am paid to be an optimist," he said.

Sen. Joseph Lieberman (D-Conn.) also sought to calm tempers but said: "It seems to me that the current division we have over policy toward Iraq is the most substantial challenge the alliance has faced since the end of the Cold War."

Meanwhile, the German news magazine Der Spiegel reported that Germany and France are working on a disarmament plan for Iraq that would include the deployment of U.N. soldiers throughout the country, reconnaissance flights and a tripling of the number of weapons inspectors, news services reported. A German government spokesman confirmed that the two countries were collaborating on a plan but would not provide any details.

Rumsfeld said he had not received official word about the proposal. "I heard about it from the press. No official word. I have no knowledge of it."

Chief U.N. weapons inspector Hans Blix, surrounded by journalists, arrives for talks at the Foreign Ministry in Baghdad. German Foreign Minister Joschka Fischer, right, talks with U.S. Defense Secretary Donald Rumsfeld before the opening of a tense conference on international security in Munich.