SEOUL, JULY 2 (THURSDAY) -- Lawmakers of the ruling and opposition parties began the task of drafting a new constitution for South Korea yesterday, after President Chun Doo Hwan, in a historic speech to the nation, gave the go-ahead for a sweeping series of democratic changes demanded by the opposition.

Spokesmen for the two parties said each side would come up with a separate draft. Negotiations will follow to produce a single document, which will then be submitted to the National Assembly.

"The most difficult points have now been agreed to," said Hyun Hong Choo of the ruling Democratic Justice Party, referring to Chun's acceptance of the opposition's demand for direct presidential elections. "The minor parts can be worked out soon."

Roh Tae Woo, chairman of the ruling party, paid a surprise visit this morning to opposition leader Kim Young Sam, who had to be summoned from a nearby office while Roh waited for about 10 minutes, opposition officials said. The two men conferred for 20 minutes, exchanging niceties, at the headquarters of Kim's Reunification Democratic Party, the officials said.

Some observers, however, are suggesting tough bargaining ahead. The two sides will be wrestling with difficult issues, such as whether the new constitution should provide for a vice president and limit the number of terms a president can serve.

Opposition leaders welcomed Chun's television address, in which he agreed to meet virtually all the demands that the opposition has been pushing for years. The demands took on fresh urgency as a result of violent demonstrations that swept the nation over the past three weeks.

Leaders said they will wait to see whether Chun actually delivers on his promises. "We must be cautious in our evaluation," senior dissident Kim Dae Jung told reporters.

Meanwhile, Kim Young Sam took a motorcade swing through Seoul yesterday in what looked like the start of a presidential campaign.

Kim called at the National Police Hospital, where 46 riot policemen are recovering from injuries suffered in street demonstrations that ended this weekend. He also stopped at a civilian hospital to see injured students.

Some political analysts have been busy looking for signs of strain between Kim Young Sam and Kim Dae Jung, the other senior figure in the opposition party.

Yesterday morning, the two Kims issued a statement declaring that they would cooperate to the fullest and see that the party fields only one candidate in the coming presidential election.

"We will by no means discard the popular wishes for our unity," Kim Young Sam was quoted as saying. In 1980, the two men fought bitterly with each other for leadership of the opposition during a turbulent political period that ended with a military takeover by Chun.

One difference in opinion between them has already been noted.

Kim Dae Jung has suggested that Chun should turn over effective power to a coalition Cabinet to supervise the election. Kim Young Sam, on the other hand, has stated that he does not feel things should be further complicated.

Chun's speech, meanwhile, continued to draw praise here and abroad.

Cardinal Stephen Kim Sou Hwan, leader of the country's 2 million Catholics, hailed it as "superb."