MOSCOW, Aug. 21, 1968 (UPI) - The overthrow of the Czechoslovak regime of Alexander Dubcek and its replacement by pro-Soviet leaders was a foregone conclusion, diplomatic sources said today.

PRAGUE, Aug. 21, 1968 (UPI) - Invasion forces from Russia and its satellites occupied Czechoslovakia with troops, tanks and jet planes against sporadic resistance today and snuffed out the country's experiment in liberal reform.Street fighting in Prague left some dead and wounded as thousands of Czechoslovaks surged into the streets and shouted defiance of the invaders.

MOSCOW, Aug. 21, 1968 (UPI) - Soviet officials, speaking through the news agency Tass, today explained why Russia and other Warsaw Pact powers had occupied Czechoslovakia.Tass said Communist Party and government leaders in Prague had asked for "urgent assistance" to meet "the threat emanating from the counter-revolutionary forces which have entered into a collusion with foreign forces hostile to socialism."

The world reacted to the Soviet bloc invasion of Czechoslovakia today with shock, dismay and condemnation. Some of the strongest protests came from Communist parties of Western nations.

WASHINGTON, Aug. 21, 1968 (UPI) - President Johnson today called on the Soviet Union and its Communist allies to withdraw their troops from Czechoslovakia. He said "it is never too late for reason to prevail.""It is a sad commentary on the Communist mind that a sign of liberty in Czechoslovakia is deemed a fundamental threat to the security of the Soviet system."

PRAGUE, Aug. 28, 1968 (UPI) -- About 3,000 students marched in the heart of Prague today behind a banner reading "No Compromise for Treason." But the Czechoslovak Government began organizing for life under Soviet Bloc occupation.