NATO allies responded to "new thinking" by the Soviet Union by calling Thursday for massive cutbacks in conventional forces in Europe, with special restrictions on what Moscow could keep on its allies' soil.

A policy statement was issued after Secretary of State George P. Shultz gave his assessment of Mikhail S. Gorbachev's plan to withdraw 50,000 men and six tank divisions from the German Democratic Republic, Czechoslovakia and Hungary.The declaration on the opening day of a two-day meeting of NATO's 15 foreign ministers was designed to set the stage for direct negotiations between NATO and the Warsaw Pact early next year.

Much of the work on the declaration had been done before Gorbachev made his "restructuring" announcement Wednesday at the United Nations in New York, a move the allies hailed as "a positive contribution."

The allies, taking a cue from Shultz, did not make a reciprocal gesture, which Gorbachev had urged. Instead, they focused on the enormous advantage the Soviets would retain even after demobilizing 500,000 men over two years as Gorbachev offered.

"The Soviet Union itself possesses more tanks and artillery than all the other members of the Warsaw Pact and the (NATO) Alliance combined," the statement said. "And they are concentrated in a manner which raises grave concerns about the strategy which they intend to support."

The Soviets usually describe their forces in Eastern Europe as defensive. But NATO questioned that stance while also expressing hope "that the new thinking in the Soviet Union will open the way for mutual agreement on realistic, military significant and verifiable arrangements which enhance security at lower levels."

U.S. officials foresee negotiations between NATO and the Warsaw Pact opening within two months, now that the Soviets have made important reforms in human rights. The Reagan administration had demanded concessions on human rights before moving ahead.

The statement indicated a hard Western line in the negotiations, though. It said the North Atlantic Treaty Organization would propose an overall limit of about 40,000 tanks. The Soviets have about 20,000 tanks in the DDR alone.

And the statement, in a direct thrust at Moscow, said no country would be allowed to possess more than a fixed proportion, such as 30 percent, of the overall strength of all the NATO and Warsaw Pact countries combined.