After an extraordinary marathon session in Brussels, NATO agreed late tonight to begin military planning for the defense of Turkey in the event of a U.S.-led war with Iraq, ending a month-long deadlock that threatened the future credibility and relevance of the military alliance.

The dispute had pitted three countries openly opposing an immediate military strike against Iraq -- Germany, Belgium and France -- against other NATO members who saw the defense of Turkey as a test of the alliance's core commitment to assist one of its members.

The impasse was broken when the issue was taken to NATO's Defense Planning Committee. France does not have a seat on the body, and the two other holdouts, Germany and Belgium, eventually gave in to pressure to accede to the formal Turkish request for help.

The decision allows NATO to begin moving alliance AWACS radar surveillance planes, Patriot missiles, and chemical and biological defense units to Turkey, to be used if Turkey is attacked during a war with Iraq.

The United States is hoping to use bases in Turkey, the only NATO country bordering Iraq, to open a northern front in a military campaign to oust the Iraqi president, Saddam Hussein. The Turkish parliament was scheduled to decide Tuesday on the U.S. request, but the foreign minister, Yasar Yakis, said today in Ankara that a decision could be delayed.

The breakthrough at NATO came when the 18-member committee agreed to a statement that said its decision "relates only to the defense of Turkey, and is without prejudice to any other military operations by NATO, and later decisions by NATO or the U.N. Security Council."

A NATO statement after the 13-hour meeting -- an alliance record -- also said, "We continue to support the efforts in the United Nations to find a peaceful solution to the crisis" over demands that Iraq give up any weapons of mass destruction.

The countries opposing the action had expressed concern that aid to Turkey could be seen as an explicit endorsement of a buildup to war with Iraq.

Belgium had wanted stronger language directly tying NATO aid for Turkey to any decision by the Security Council to authorize war with Iraq. But others, led by the United States, Britain and Canada, which proposed the final wording, resisted the effort.

"The United States felt very strongly, as did many other allies, that NATO's decision-making could not be subordinated to the United Nations," a senior NATO official said.

NATO officials described today's closed session as remarkable. Eighteen ambassadors in the room negotiated indirectly with the Belgian prime minister, Guy Verhofstadt, who was called more than a half-dozen times during the talks and who then had to consult with his governing partners before agreeing to the final terms. The diplomatic advisers to the Belgian prime minister and the country's foreign minister, Louis Michel, were in the room during the talks.

The U.S. ambassador, Nicholas Burns, applauded the decision tonight, saying, "What was at stake over the past several weeks was NATO's credibility, and NATO passed that test today when 18 members, except France, agreed to assist Turkey."

France has not been a member of the Defense Planning Committee since President Charles de Gaulle pulled the country out of NATO's integrated military command in 1966. The committee has rarely been used since the end of the Cold War. In 1991, it ruled on a similar issue of using NATO assets in Turkey in the Persian Gulf War.

A senior NATO official, who called the French position "obstreperous," said, "It was France's decision [in 1966] to exclude itself."

He added: "France is isolated on this. The axis of three countries has been broken up."

Some NATO countries, such as the Netherlands, were already moving to aid Turkey even without a NATO decision. The center-right Dutch government has been a key ally of Washington's, and a defense spokesman today said that four of the country's Patriot anti-missile batteries, manned by about 400 Dutch soldiers, had already been shipped to Turkey on a bilateral basis and would be operational by early March.

The stalemate had threatened to undercut NATO's credibility as a mutual defense organization, and some U.S. administration officials and lawmakers had bluntly warned that the alliance risked becoming irrelevant if it failed to act on Turkey's request for help.