BRUSSELS, NOV. 30 -- Defense Secretary Frank C. Carlucci, here to meet with European defense ministers before next week's superpower summit, said today that the United States will have to become "more creative" in its conventional military support of NATO.

Carlucci and other senior U.S. officials said tighter budgets are threatening U.S. contributions to the North Atlantic Treaty Organization at a time of high allied demands for conventional military support -- because of the pending agreement to reduce intermediate-range nuclear weapons in Europe.

"That's now the top-priority item we have to address," said a senior Pentagon official involved in the semiannual NATO Defense Planning Committee meeting, which begins here Tuesday.

But Carlucci said the United States is going to have to meet those new demands by being "more creative" because putting more money into NATO defenses "is going to be a problem."

Carlucci said the United States is considering options ranging from "terrain enhancements" -- barriers that would help reduce the need for some troops -- to improved cooperation in air defense.

He also said that he expects "force structure to be a big political debate in the U.S. . . . but those who think this is the beginning of decoupling {pulling back troops} are just plain wrong."

Defense Ministers of 12 West European countries, meeting here today prior to the NATO meeting, welcomed the U.S.-Soviet accord as a "historic step toward the realization of a longstanding alliance objective," while expressing concern about the implications for their conventional defense.

Carlucci, on another issue, told U.S. reporters that most of the $30 million in supplemental aid the Reagan administration has requested for the Nicaraguan rebels would be used for electronic countermeasures equipment to help protect their aircraft.

"The Sandinistas are getting much more sophisticated in being able to shoot down the airplanes," Carlucci said of the Nicaraguan government forces that are battling the U.S.-backed rebels.

Reuter reported from Oslo:

Norway's former prime minister, Kaare Willoch, has withdrawn his candidacy for the post of NATO secretary general, a Foreign Ministry spokesman said.

The withdrawal leaves the way open for Willoch's rival, West German Defense Minister Manfred Woerner, when Britain's Lord Carrington steps down next year as NATO chief. West Germany and Norway have been involved in a public dispute over the top NATO post.