The meeting is Rumsfeld's first at NATO since the Sept. 11 attacks in New York in Washington, and fellow defense ministers are eager to hear his views on the next step in the campaign.
It is also the first occasion allied defense ministers have had to talk with a top American official since the United States announced its intention to abandon its 1972 Anti-Ballistic Missile treaty with Russia, a subject that worries many of Washington's friends.
has invoked Article 5 of its founding treaty, declaring that the attacks on the United States in September should be treated as an attack on all 19. But the alliance has had no front-line role in the war in Afghanistan and none is envisaged.
Though a 1999 strategic plan developed by NATO points to terrorism and the spread of weapons of mass destruction among the major threats facing NATO in the future, the alliance is still heavily geared toward fighting wars of territorial defense and not the shadowy forces of terror.
Russian Defense Minister Sergei Ivanov also is in Brussels and will be talking with NATO about plans for closer relations between the former adversaries.
Rumsfeld met with Ivanov separately Monday night.
Earlier this month, NATO foreign ministers launched a plan for closer relations with Moscow, instructing alliance officials to begin developing new council where Russia could join with the allies in discussion, planning and even decision-making on specific subjects. Work is expected to be completed by next spring.
The defense ministers will begin to consider the subject matter that the new NATO-Russia council might cover, the senior official said.
Also on the ministerial agenda is the Balkans, where the alliance is leading about 60,000 troops in three separate military operations, in Bosnia, Kosovo and Macedonia.
The defense ministers will be looking at ways to make the Balkans operations more efficient, and, eventually, to reduce their size.
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