LONDON, March 1--Prime Minister Harold Macmillan will return from Moscow tomorrow determined to urge the Western Allies into a summit conference as the only way of removing the Soviet threat to Berlin, responsible British sources said.

He was reported convinced that East-West negotiations without Nikita Khrushchev at the table would be pointless.

A further factor cited was belief that a summit conference offers the most dramatic means of impressing on Khrushchev the NATO resolve that West Berlin stays free despite Soviet threats to neutralize it and turn over control of its traffic with the West to Communist East Germany his talks with Khrushchev.

Macmillan underlined this resolve in

Two London newspapers in close touch with official thinking, the Sunday Times and the Observer, reported that Macmillan will urge President Eisenhower and President Charles de Gaulle of France to go with him to the summit.

Mansfield Fearful of Crisis

WASHINGTON, March 1--Congressional concern mounted today over the possibility the Soviet Union may start a war over Berlin.

Sen. Mike Mansfield (D-Mont.) voiced fear Soviet Premier Nikita Khrushchev might "do something on the spur of the moment" that would ignite a conflict.

Mansfield, assistant majority leader of the Senate, said Khrushchev would not start a war deliberately, although he said it is "always possible" he might risk one.

Mansfield said "I think he--Khrushchev--cannot be trusted not to do something on the spur of the moment" that would start a shooting war.