NATO Unveils Plans for Expansion : Military: Strategy maps extension of U.S. nuclear umbrella and higher costs for member countries.

The Atlantic Alliance on Thursday presented its blueprint for a controversial expansion that would commit the United States and its NATO allies to defending large new areas of Central and Eastern Europe--with nuclear weapons, if necessary.

For the first time, the plan sets down on paper what few besides defense experts have grasped: Enlargement means a significant extension of the United States’ nuclear umbrella.

“The coverage provided by [the NATO security guarantee], including its nuclear component, will apply to new members,” states the 28-page document.

NATO members’ defense budgets are sure to rise to support such a dramatic extension of security commitments.

But the study stresses that expansion would not necessarily mean repositioning of the North Atlantic Treaty Organization’s nuclear arsenal.

“There is . . . no need now to change or modify any aspect of NATO’s nuclear posture or policy, but the longer-term implications of enlargement for both will continue to be evaluated,” the study concludes.

The document was handed to representatives of the alliance’s 26 “cooperation partner” countries who had gathered at NATO headquarters here. Many partner nations, such as Poland, the Czech Republic and Hungary, are prospective new members.

Russia’s ambassador to Belgium, Vitaly I. Churkin, sat quietly through the presentation, but his comments to reporters afterward left little doubt that Moscow remains deeply opposed to NATO’s eastward expansion.

“We are still against it,” Churkin said. “Feelings are very strong about this in Russia.”

Churkin’s reaction came despite a long passage in the study acknowledging the importance of Russia’s role in European stability and stressing NATO’s desire for good relations with Moscow.

“We’ll continue to make efforts to strengthen our relations with Russia,” said NATO Secretary General Willy Claes at a news conference. “We can’t imagine a strong, credible security architecture in Europe without Russia.”

Moscow’s vehement opposition to NATO enlargement is one of several factors that have made the expansion idea highly controversial.

Many Western defense specialists insist that building good ties with Russia is far too important to be jeopardized by an expansion of questionable need.

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The document released Thursday addresses the “how” and “why” of enlargement, but not the “who” or “when.” After weighing the reaction of potential members during the next few months, NATO foreign ministers are expected to decide the next step in the expansion process when they convene here in December.

What that step might be, however, is unclear, especially since the issue of expansion has been neither seriously debated nor well understood by the publics of most member countries.

In the United States, for example, enlargement stands as the lone foreign policy item in the Republican Congress’ “contract with America,” yet few of those who endorse it have come to grips with the fact that it will mean increased defense spending and a dramatic expansion of U.S. security commitments.

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Rep. Lee H. Hamilton (D-Ind.), ranking minority member of the House International Affairs Committee, predicted that the proposal unveiled on Thursday ultimately will spark a brouhaha in Congress.

“These [former Soviet Bloc] countries, after all, have a long history behind them,” he said in a telephone interview. “I think you’re going to have quite a debate on this whole issue.”

In many ways, the study is as much a NATO vision of European security in the 21st Century as it is a framework for expansion.

The document sketches a Europe in which:

* A large number of like-minded democracies band together under the NATO umbrella to face the new threats of a post-Cold War era, sometimes engaging in peacekeeping operations of the United Nations and the Organization for Security and Cooperation in Europe.

* Enlargement follows closely the expansion path of the European Union, and the two organizations cooperate closely to support stability and integration.

* NATO and Russia work together in a “constructive, cooperative” relationship.

Times staff writer Art Pine in Washington contributed to this report.