Moscow will begin its unilateral withdrawal of 50,000 troops from Hungary, Czechoslovakia and East Germany in April, a senior Soviet defense official was quoted as saying.

Deputy Defense Minister Vitaly Shabanov said the withdrawal announced last month by President Mikhail S. Gorbachev will occur in two phases, Austrian Television's Moscow correspondent reported Monday.The first phase will be completed this year, the second in 1990, Shabanov was quoted as saying. "We assume it will begin in the coming April," he said.

In a Dec. 7 speech to the U.N. General Assembly, Gorbachev said 50,000 troops and 5,000 tanks would be withdrawn from Eastern Europe as part of a worldwide cut in the Red Army of 500,000 troops - nearly 10 percent of its more than 5 million personnel.

Communist Party leader Karoly Grosz of Hungary was quoted as telling a Japanese newspaper last week that the withdrawal of Soviet troops from his country would begin within weeks but fixed no date.

In Prague on Monday, Soviet Ambassador Vladimir Lomakin announced that one Soviet division - roughly 12,000 troops - would soon be withdrawn from Czechoslovakia. An estimated 80,000 Soviet troops are stationed in the country.