WASHINGTON (AP) _ The United States will begin looking for another NATO nation in which to base a wing of F-16 fighters after acceding to a demand from Spain that the 72 jets be moved.

State Department officials indicated Friday that southern members of the North Atlantic Treaty Organization probably will be asked if they are willing to accept the planes, the 401st Tactical Fighter Wing, located at Torrejon Air Base outside Madrid.

Italy and Turkey would be among the chief candidates. Greece is not likely to be asked since that nation has threatened to expel U.S. forces from Greek bases when a U.S.-Greece agreement expires.

NATO defense plans call for using the F-16s, which are among the world's best fighter-bombers, to help protect the southern tier of nations in the alliance, stretching from Spain to Turkey.

The announcement Friday that the United States would remove the fighters from the Torrejon base came after 18 months of negotiations during which the two countries also agreed in principle on a new, eight-year-lon g defense pact between the countries. Further discussions to finalize the pact begin Feb. 3.

The F-16s, along with 4,000 U.S. servicemen, will be withdrawn from Spain within a three-year period after a final defense pact agreement goes into effect.

State Department officials tried to put the best face on the agreement announced in a joint statement by the two countries, saying there are ''important pluses'' in it.

Spokesman Charles Redman said, ''If the question is, 'Does NATO strategy remain viable? Is NATO safe?,' then the answer is yes.''

But at the Pentagon, officials were more pessimistic and indicated that the planes likely will end up back in the United States.

''This is going to leave a hole in NATO defenses that the Spaniards are not equipped to fill; that's the bottom line,'' said one official who spoke on condition of anonymity. ''And NATO better get serious about it. This is not a hole that the U.S. created. We're not withdrawing support for the alliance; we're getting kicked out.''

There was no immediate reaction from Capitol Hill, since Congress won't be in session until Jan. 25. But last fall, angry legislators voted to ban using any U.S. money to move the planes to another NATO nation. That means that other NATO countries would have to pay for any relocation of the jets.

The agreement leaves other U.S. facilities intact in Spain, including air bases at Zaragoza and Moron, a major U.S. Navy station on Spain's Atlantic coast at Rota, and nine communication posts.

The two nations had been negotiating on a new base agreement since 1986 and U.S. officials tried unsuccessfully to keep the planes at Torrejon. Spanish voters approved a 1986 referendum which kept Spain in NATO but which ordered a sharp cut in the U.S. military presence as the price.

Prime Minister Felipe Gonzalez's government called for the F-16s to be removed and said their withdrawal was a precondition to a new bilateral defense treaty.

Spanish Foreign Minister Francisco Fernandez Ordonez said in Madrid that his nation had dropped a demand that the Air Force also should withdraw five KC-135 aerial refueling tankers from northeastern Spain.

''Spain's desire has been, and continues to be, maintaining a stable, balanced and mature relationship with the United States,'' he said.

U.S. troops have been stationed in Spain since 1953, when President Dwight Eisenhower and Gen. Francisco Franco signed the first U.S.-Spain defense agreement.