BRUSSELS, Belgium (AP) -- NATO foreign ministers today began revising the political and military principles that have guided the 16-nation alliance for half a century.

The ministers are laying the groundwork for an anniversary summit in Washington in April, where leaders are expected to approve the alliance's security doctrine for the 21st century and welcome three new members -- Poland, Hungary and the Czech Republic -- into the fold.

``One of the special qualities of the alliance has always been its ability to react flexibly to new situations,'' German Foreign Minister Joschka Fischer told fellow ministers. ``On the eve of the 21st century we should ask ourselves if our instruments still match the changed security environment.''

Today's threat is no longer a Russian tank assault across the plains of Central Europe, but challenges from regional conflicts like Bosnia and Kosovo, terrorism and the spread of weapons of mass destruction. When these threats originate from outside NATO's traditional territory of operations, the alliance must be prepared to deal with them.

In practice, NATO has already adjusted to these new realities, intervening in Bosnia, halting the humanitarian disaster in Kosovo with the threat of air strikes, sending soldiers just across the Kosovo order in Macedonia to rescue civilian cease-fire monitors if needed.

``Today we will be discussing the future of NATO and how we are going to do it in the next century,''

said British Foreign Minister Robin Cook.

He said Europeans should work through NATO in their effort to play a greater role in European security issues, particularly in cases where the United States is less interested in participating.

``I want to make it clear today that what we want to see is improvement of security in Europe and strengthening of NATO,'' Cook said.

Secretary of State Madeleine Albright, writing in the British newspaper The Financial Times, said: ``NATO's primary mission will always remain defense against aggression. But the founders of the alliance also distinguished between what the treaty commits us to do and what it permits us to do.''

She said Bosnia and Kosovo are recent examples ``that demonstrate NATO must act when conflicts beyond its immediate borders affect alliance interests. NATO must find the right balance between the centrality of NATO's collective defense missions and responding to such crises.''

NATO's central mission will always be collective defense and the concept that an attack against one member is an aggression against all. But attacks against members now take different forms and often originate far away.

Albright planned to propose at the ministerial meeting here setting up a Center for Weapons of Mass Destruction, officials said.

The plan would use NATO headquarters staff under one director, with perhaps a few extra experts, they said.

The Germans plan to bring up the nuclear first-strike question later in the meeting.

Fischer made waves when he called on NATO last month to consider dropping its doctrine allowing a nuclear first-strike. This doctrine, reaffirmed as recently as last year, has always been a part of NATO's nuclear strategy and is considered an important aspect of deterrence.

``The minister will certainly raise the issue,'' a German diplomatic source said. ``We have to see that in the context of arms control, arms reduction and nonproliferation.''

The Germans don't have much backing on the issue, however.

The allies were to assess the situation in Kosovo, where Serb security forces and ethnic Albanian guerrillas clashed for seven months. The threat of a NATO air strike stopped the fighting in October and the cease-fire is generally holding, while American mediator Christopher Hill attempts to firm the peace with political agreement.

The ministers also were to make their six-monthly review of the situation in Bosnia. No major reduction in the 32,000-troop level in the NATO-led peacekeeping force is expected soon.

Copyright C 1998 Associated Press Information Services, all rights reserved.