BRUSSELS, DEC. 11 -- America's European allies today hailed the agreement to eliminate medium-range missiles from Europe, signed Tuesday by President Reagan and Soviet leader Mikhail Gorbachev, as "a treaty without precedent in the history of arms control."

Foreign ministers of the 16-nation North Atlantic Treaty Organization put that language in the opening sentence of a communique after hearing a detailed briefing by Secretary of State George P. Shultz about the Reagan-Gorbachev summit in Washington earlier this week.

Behind the public praise for the intermediate-range nuclear forces (INF) treaty removing nuclear-tipped, medium-range and short-range missiles from the U.S. and Soviet arsenals, there was some grumbling, notably by France, about new problems that the accord might create for the defense of Western Europe.

NATO sources said, for example, that the communique's glowing language about the treaty was watered down somewhat by France's refusal to permit use of the word "historical" in the description.

Another looming conflict within NATO appeared over the question of modernizing the remaining battlefield nuclear weapons along the East-West divide.

The modernization of NATO's array of short-range nuclear weapons, whose range of less than 300 miles leaves them exempt from the INF treaty, is considered by many allies as an important new step to retain a plausible nuclear option and to counter the perceived Soviet superiority in conventional forces.

But the improvement of battlefield nuclear weapons has become an increasingly delicate issue in West Germany, where there is powerful and growing political opposition to enhancing weapons that would most likely strike German soil in a nuclear exchange between NATO and Warsaw Pact forces in Central Europe.

As a high priority in the next phase of East-West arms negotiations, German officials have suggested establishing strict new limits on deployment of the short-range nuclear arms.

The United States and Britain have indicated, however, that those NATO nuclear arms still permitted in Europe under the INF treaty should be improved to offset the loss of Pershing II and ground-launched cruise missiles as mandated in the new agreement.

In West Germany, this plan would focus primarily on modernizing the short-range Lance missile. Senior officials of NATO countries, particularly British Prime Minister Margaret Thatcher, also have suggested that improving air-launched cruise missiles, which could be fired from American aircraft flying near the East-West frontier, might be another way of making sure western defenses do not suffer because of the treaty.

In a television interview last night, Thatcher said the Soviet Union was improving its cruise missile capabilities. Western nations, including Britain, also must modernize their weapons systems permitted under the treaty, she insisted.

"I have not, in fact, ever heard the Russians say that it would undermine the treaty {to improve cruise-missile forces}," Thatcher told an interviewer on Britain's Independent Television News. "What I do know is that the Russians are working very hard on cruise missiles of all kinds. . . . They will be expecting us to do the same thing."

French Foreign Minister Jean-Bernard Raimond, echoing the views of the United States and Britain, said today at the NATO meeting that strategic, or long-range, weapons and conventional forces should be the focus of any new reductions, rather than the West German emphasis on battlefield nuclear weapons.

"The good procedure is to start with reductions in strategic arms rather than insisting on talking about steps that would lead to the denuclearization of Europe," he said.

NATO Secretary General Lord Carrington said the alliance has undertaken a broad review of the connections between nuclear and conventional forces in an effort to forge a united NATO stand on conventional and chemical arms negotiations.

Despite the differences among the NATO allies, U.S. officials insisted that the dominant attitude was one of enthusiasm and that the major anxiety of the Europeans is that the U.S. Senate might not ratify the treaty speedily.

"They read about people in the United States questioning the treaty, and it causes concern. The sentiment in the communique is strong and unambiguous that people in the alliance want to see this treaty take effect," Shultz told reporters.

Shultz also took an indirect swipe at American conservatives who have charged that European governments fear the treaty will tip the nuclear balance in the Soviet Union's favor.

"My European colleagues take particular umbrage at Americans who presume to speak for Europe and say the Europeans don't want this treaty. As the Norwegian minister {Thorvald Stoltenberg} told the meeting, 'If you want to know what Norway thinks, ask the Norwegians,' " Shultz said.

"This is a very good treaty that comes out of an alliance concept and that achieves what we set out to achieve," the secretary added.

The signing of the INF treaty capped a negotiating process set in motion eight years ago, on Dec. 12, 1979, when NATO, concerned by Soviet deployment in Eastern Europe of 2,500-mile-range mobile SS20 missiles, voted to base U.S. cruise and Pershing II missiles in Britain, West Germany, Italy, Belgium and the Netherlands.

But NATO made the American deployment part of a two-track strategy under which the missiles would be removed if the Soviets agreed to get rid of their SS20s.

In the ensuing years, that approach withstood a strong Soviet propaganda attack, peace movement protests that created political turmoil in the countries where the missiles have been based and a succession of on-again, off-again negotiations between Washington and Moscow, resulting in the treaty signed at the White House Tuesday.

The long road that NATO traveled to reach that point was underscored symbolically today when Shultz and foreign ministers of the five basing countries gathered to sign an accord clearing the way for the Soviets to inspect U.S. missile sites on their territory as part of the treaty's complex verification procedures.

The five ministers all called this week's events a sign, as West German Foreign Minister Hans-Dietrich Genscher said, of "how the alliance can make its policies prevail if it remains united and decisive."

In another action, the ministers formally announced that West German Defense Minister Manfred Woerner will take over next July as NATO's new secretary general, succeeding Lord Carrington, who is retiring.