Czechoslovakia began talks today with the Soviet Union on the withdrawal of about 75,000 Soviet troops, and one source said Czechoslovak officials want at least half of the force out by May. On the eve of the talks, about 6,000 people protested in the town of Pohorany, demanding the entire Soviet force leave by Aug. 21 _ the 22nd anniversary of the Soviet-led invasion that crushed the Prague Spring reforms. Foreign Ministry spokesman Lubos Dobrovsky said last week that the Soviet forces should leave Czechoslovakia by the end of the year. ``The idea is to have them (Soviets) make a political commitment during these talks that all the troops will leave by the end of the year,'' the source said on condition of anonymity. ``The rough idea of the time frame on the Czechoslovak side is to see a 50 to 60 percent withdrawal by mid-May,'' the source said, adding the talks should focus on technical details of the pullout as well as its precise timing. No details emerged from the talks, led by Deputy Foreign Minister Evzen Vacek and his Soviet counterpart, Ivan Aboimov. The source said demands for the complete withdrawal before Aug. 21 were ``technically out of the question.'' He noted it took a year to withdraw 5,300 soldiers, 708 tanks and 200 planes from Czechoslovakia in 1989 as part of a Kremlin move to withdraw about 50,000 troops from Eastern Europe. A peaceful revolution in November and December toppled the hard-line Communist government. Dissident playwright Vaclav Havel is now president and Alexander Dubcek, the former Communist Party chief who sponsored many of the Prague Spring reforms in 1968, is head of Parliament. In another development today, a South Korean government delegation arrived in Prague to discuss establishing diplomatic relations, the state CTK news agency reported. The delegation was invited by the Foreign Ministry, CTK said. South Korea, which is staunchly anti-Communist, has established formal diplomatic ties with Hungary, Poland and Yugoslavia in recent months. In December, South Korea and Czechoslovakia agreed to open trade offices in each other's countries.