BERLIN, Nov. 28--Mayor Willy Brandt today won firm backing from Western leaders in his fight against the Soviet attempt to turn West Berlin into an unarmed neutral city.

Diplomatic reports pouring into West Berlin indicated the United States, Britain and France would reject the Soviet maneuver. U.S. congressmen visiting the isolated city assured the fighting mayor staunch U.S. support.

The West Berliners, heartened by such outside support, defied grim Red hints of trouble when Moscow's six-month period for accepting the neutral city proposal expires.

Communist East Germany's Premier Otto Grotewohl welcomed the Soviet plan, as a great concession to the West. Grotewohl, in a statement, reminded West Berliners that his regime is not backing off on its claim that all Berlin belongs to East Germany.

He said his regime would assure West Berlin of free lines of communications if West Berliners accepted the Soviet plan.

Defense Spending May Rise

AUGUSTA, Ga., Nov. 28--Secretary of Defense Neil H. McElroy, after conferring with President Eisenhower today, left open the possibility military spending next year will run a billion dollars more than this year's estimated $40,800,000,000.

With Eisenhower striving to cut overall federal spending, McElroy's remarks at an airport news conference by no means brightened the prospect of success.

"We are going to have a pretty rough time trying to avoid" a military outlay hike in the fiscal year starting July 1, McElroy said.

Asked about the possibility of a two-billion-dollar increase, McElroy shot back: "Oh, no, I don't think that much."

About a billion-dollar jump he said: "I don't know."

He stressed, however, that every consideration is being given to maintaining a sound national economy generally--as well as a strong military position.