America’s Nuclear Umbrella Is Still Vital, 2 Allies Say : Europe: Britain’s Thatcher and West Germany’s Kohl differ about the Continent’s political future. But both favor basing nuclear weapons there.

Two of the United States’ most important Western allies differed publicly over key aspects of Europe’s political future here Friday but agreed that America’s nuclear umbrella remains essential to the Continent’s ultimate security.

West German Chancellor Helmut Kohl and British Prime Minister Margaret Thatcher, whose relations are notoriously tepid, appeared to go out of their way to be jovial at a joint press conference concluding two days of official talks here. But beneath the laughter, some of their differences were too great to paper over.

Where Kohl urged faster progress toward European political union, Thatcher said she wanted to keep things pretty much the way they are.

Where Kohl urged greater powers for the European Parliament in Strasbourg, Thatcher said she saw “no need for any further increase” in its authority.

Where Kohl was clearly cool toward plans to modernize the North Atlantic Treaty Organization’s short-range nuclear weapons in Europe, Thatcher said the issue still had to be resolved among the NATO allies.

There was even some ambiguity regarding the need to base nuclear weapons in a united Germany.

“We both agree that the presence of nuclear weapons on European soil--and I think German soil is the preferred soil--is vital,” Thatcher told reporters Friday. That remark seemed more tentative than her insistance in a speech the night before that “NATO should continue to have nuclear weapons based in Germany.”

British officials tried to play down the significance of the difference.

“We don’t think it’s any change in tone or anything,” said one.

However, the question of Western nuclear weapons remaining in a unified Germany is crucial in the so-called two-plus-four talks concerning the international ramifications of reunification. Participants in those talks include East and West Germany and the four major victorious World War II powers, Britain, France, the United States and the Soviet Union.

Moscow still insists formally that a united Germany be neutral, although some Soviet and other analysts have suggested it might more readily accept NATO membership for the unified state if it were free of nuclear weapons.

American aircraft armed with nuclear missiles are based in other NATO member countries.

Kohl reassured Thatcher that he is committed to NATO membership.

“The future united Germany must . . . remain embedded in the Western alliance,” he said in dinner remarks Thursday. “Secession from NATO must not be the price for German unity. Such a policy is not acceptable to me.”

And Friday, he stressed once more that “I think in the future, too, we need full protection for the territory of Germany from NATO.”

On the question of short-range nuclear weapons, however, he stressed that “the world has changed. If you consider the range of these weapons, then you’ll see that they can reach cities like Warsaw, Prague, and Leipzig, or the East German city of Rostock where I recently spoke before a crowd of 100,000 people.”

Kohl politely needled Thatcher several times during the talks here over her lack of enthusiasm for a politically unified Europe. She is loathe to cede what she considers key elements of national sovereignty to a European bureaucracy based in Brussels or Strasbourg.

If they do not band together politically, the nations of Europe will have insufficient influence on the fast-changing, post-Cold War world, said Kohl. He has promised to call for talks later this year aimed at “faster progress toward political union.”

The German leader also pointedly recalled both Thursday and Friday the vision once expressed by the late Winston Churchill of a “United States of Europe.” Thatcher reveres Churchill, who was Britain’s World War II leader but vigorously opposes the creation in Europe of a U. S.-style federation of states.

Thatcher argued that there is already “very good and increasing political cooperation” among the nations of Western Europe. “We each of us willingly cooperate, each of us keeping our own pride, our own natural pride, our own history, our own identity, our own characteristics which we bring together to Europe as a whole. I believe that Europe is growing together in that way, in willing cooperation, and I believe that it is growing day by day, and that is the way I would like to keep it.”

In a forgetful moment, the forceful British leader saw no need to consult with her German guest on a question regarding Germany’s border with Poland. After answering it herself, she began to dismiss the press before realizing that perhaps the chancellor might have a word or two to add.

“No,” he responded to the embarrassed Thatcher with a laugh, “that was a perfect answer.”