WASHINGTON, March 6--The four men who lead Congress met for 90 minutes with President Eisenhower today and promptly proclaimed bipartisan backing of his firm stand against Red threats to Berlin.

"The Communists will discover that this country and our free allies are determined to preserve the free world," Senate Democratic Leader Lyndon B. Johnson of Texas said.

"We are unified; we don't have any parties in this thing," Speaker of the House Sam Rayburn (D-Tex.) said. "A common and unified posture," Senate Republican Leader Everett M. Dirksen of Illinois added.

House Republican Leader Charles A. Halleck of Indiana emphasized that this did not mean a firmness which barred a negotiated settlement.

Prime Minister Reports Progress on Disarmament

BELFAST, Northern Ireland, March 6--Prime Minister Harold Macmillan said today that he and Soviet Premier Nikita Khrushchev, canvassed "possible ideas of disarmament" in their Kremlin talks and made some progress.

There exists a vast chasm between East and West, however, "on the great issues of European security, of Germany and of Berlin," he told a meeting of political supporters.

"The immediate result of our visit to the Soviet Union," Macmillan continued, "may be said not to have been very great.

"I would not myself claim more than that we have much improved our knowledge of each other's points of view and so perhaps paved the way to negotiation in a wider circle."

Contact With Pioneer Lost

WASHINGTON, March 6--The radio aboard America's sun satellite faded out today, and a space agency spokesman said "Pioneer IV is gone forever."

A powerful government radio telescope lost contact with the 13-pound cone at 10:24 a.m. EST. The General Electric Co. tracking station at Schenectady, N.Y., reported flickering signals until shortly after 11:30 a.m.