At a summit meeting to create rules by which an expanded Europe will operate, the leaders of the 15-nation European Union adopted a common security strategy today to enable Europe to “share in the responsibility for global security and in building a better world.”

Giving the strategy teeth, the European Union approved a plan that has aroused misgivings in Washington in the past for a military planning staff separate from NATO.

The 14-page strategy paper, based on a draft by the chief European foreign affairs official, Javier Solana, emphasized that “the trans-Atlantic relationship is irreplaceable.”

“Acting together, the European Union and the United States can be a formidable force for good in the world,” the European Union document said. “Our aim should be an effective and balanced partnership with the United States.”

While distancing itself from the pre-emptive security thinking of the Bush administration, the document cataloged present threats to peace, including terrorism, weapons of mass destruction, the collapse of government institutions and organized crime. In the post-Cold War era, it concluded, “none of the new threats is purely military, nor can they be tackled by purely military means.”

The document sweetened the pill of a common European force long envisioned by European leaders to allow Europe to formulate a defense policy separate from that of the North Atlantic Treaty Organization, which the United States dominates.

The vision gained force after the Treaty of Maastricht, which took effect in 1993, mandating gradual progress from mere economic integration to common policies in defense and foreign affairs.

The moves today came at the outset of a two-day meeting at which the Union’s leaders were joined by the leaders of 10 countries, mainly in Eastern Europe, that will join the European Union next year, to try and break a deadlock over a new draft constitution for the enlarged union. The discussions, which may spill over to Sunday, will center on differences over voting procedures and the future role of the Council of Europe, which unites the heads of government.

The moves were preceded by weeks of intense diplomatic effort to diminish American resistance, particularly at meetings this month in Brussels with Secretary of State Colin L. Powell and Defense Secretary Donald H. Rumsfeld. Both men had opposed such a policy as an unnecessary duplication of NATO, which already pools European military resources under a single command.

President Jacques Chirac of France, a staunch proponent of an independent European defense policy, praised the moves as a “confirmation of European defense, an affirmation of its interests.” At a news briefing, he said Europe was “obliged to have organized means of defense.” But he was at pains to stress the integrity of NATO, saying the plan was in “perfect conformity with the demands of NATO.”

Mr. Chirac said that debate with the United States over a European force had been “considerably polluted” by the differences over the war in Iraq.

The United States was angered earlier this year when four European Union nations — France, Germany, Belgium and Luxembourg — promoted the idea of a separate European military headquarters independent of NATO. The French and the Germans, under pressure from Prime Minister Tony Blair of Britain, revised the plan to accommodate American objections.

Several leaders said the group had discussed the United States’ decision this week to exclude countries opposed to the war, including France, Germany and Russia, from reconstruction contracts in Iraq, though it reached no consensus.

Mr. Blair later defended the United States. “It is very important to emphasize that this is American money,” he said, adding that it was “for the Americans to decide how they spend their money.”

Mr. Chirac, emphasizing the need for “adhesion in the international community” in facing the challenges of Iraqi reconstruction, said the United States should ask whether such exclusions “go in the direction of indispensable unity, or of disunity.” Yet he said he was prepared to meet former Secretary of State James A. Baker III, who will visit Europe next week to discuss debt relief for Iraq.

Germany’s foreign minister, Joschka Fischer, said the Europeans had to convince not only the United States but also Canada. “NATO remains indispensable for our collective defense,” he told reporters.

Mr. Blair, addressing reporters, said the move provided the “opportunity to keep the trans-Atlantic American alliance very strong,” while assuring that “where vital European interests are involved, that Europe can act.” The plan, he said, was “completely consistent with NATO as the cornerstone of our alliance.”