SEOUL, SEPT. 2 -- The leaders of South Korea's ruling and opposition parties pledged today to hold elections by Dec. 20 and seek speedy liberalization of the country's labor laws, as workers began new protests at the giant Hyundai factories.

Roh Tae Woo, ruling party chairman, and Kim Young Sam, president of the major opposition party, talked amicably in the National Assembly building for almost three hours and agreed on a timetable for what would be the nation's first contested election since 1971, their spokesmen said. Roh is the likely ruling party candidate, and Kim is one of two chief contenders to represent the opposition.

The meeting itself was heralded as an auspicious event in South Korea, where the government has arrested opposition politicians more often than it has negotiated with them in recent years. The two leaders had substantive talks for the first time since the government, in response to widespread street protests in June, promised direct elections and other reforms.

The talks took on special urgency in light of the continuing labor strife. Workers have staged strikes or sit-ins at more than 2,000 plants since June 29, when Roh took to national television to urge President Chun Doo Hwan, his friend and former Army colleague, to accede to opposition demands. Chun agreed on July 1.

Most strikes have been settled after only a few days, but at Hyundai's factories in the eastern coast city of Ulsan -- scene of the summer's largest strikes two weeks ago -- trouble broke out again today.

Tens of thousands of Hyundai workers returned to work last month after the company recognized their newly formed unions and promised to weigh their requests for wage increases. No wage agreement was actually reached in the preliminary settlement, which was mediated by a Labor Ministry official.

Today, the postponed issue of wage increases returned to the surface as between 20,000 and 30,000 workers staged sit-ins and then marched through Ulsan, driving commandeered forklifts, trucks and tractors and holding a rally in the city's stadium.

Other workers gathered in front of Ulsan's city hall, where some smashed windows and burned about a dozen municipal vehicles.

Workers originally requested a 25 percent increase in basic wages, while management offered a 7 percent raise. Both sides had moved toward compromise by today, but talks broke off without agreement this morning.

The Hyundai conglomerate's 11 companies produce steel and build ships and Excel automobiles that are exported to the United States, among other products. The outcome of its labor dispute has been cited as an important precedent for smaller, lesser known companies.

Hyundai Motor Co. was not affected by today's disputes, but strikes at parts suppliers threaten to interrupt car production in two or three days, company officials said.

A taxi strike lasted a second day in Seoul today, with isolated reports of violence between striking drivers and owner-drivers who continued to work. At least seven drivers were arrested, police said.

Roh and Kim said they would urge their party members in the National Assembly to act quickly to revise the nation's labor laws, widely considered to favor management. They said the legislature should guarantee the rights to form unions, bargain collectively and strike.

Those three basic rights are included in a draft constitution agreed on by lower ranking party officials Monday after a month of negotiations. But Roh and Kim said the rights should be enacted as soon as possible, before the new constitution takes effect.

The two leaders hailed the draft constitution and agreed that the National Assembly should approve it by early October, sending it to a national referendum late that month. Approval then would allow presidential elections to take place in early or mid-December and, in any case, no later than Dec. 20.

The two men did not agree on all points. Kim pressed for release of more political prisoners but won only an agreement to discuss the issue further at another session.

They also disagreed on when National Assembly elections should be held, with Kim favoring December and Roh February.

President Chun, meanwhile, assured Sen. Alan Cranston (D-Calif.) that the military will not intervene in the political process, the visiting senator told news media.