SEOUL, AUG. 22 (SATURDAY) -- Thousands of city bus drivers spurned their union leaders' recommendation today and rejected a wage increase offer that top South Korean officials had helped negotiate in hopes of averting a crippling strike.

The rejection by some, but not all, drivers showed the volatility of the current labor situation in South Korea and once again raised the possibility of a destabilizing strike in the capital.

The news came as President Chun Doo Hwan threatened to crack down on "leftist subversives" who he said represent "the most serious threat to democratic development."

Chun, in what was billed as his last annual press conference before becoming the first South Korean head of state to cede power peacefully, said he believes the nation is on track to hold elections in time for him to resign in February. But he warned that "if a handful of such subversives try to agitate the public . . . the government will take resolute action under the law to ensure national security and survival."

Drivers at 21 of the 89 private bus companies that serve the Seoul area voted to strike immediately, according to news reports this morning. At another 52 companies, drivers rejected the settlement package and said they will strike in five days unless better terms are offered.

{Tens of thousands of morning rush-hour riders were stranded in Seoul, The Associated Press reported. The surprise walkout caused confusion in many areas, sending commuters rushing to nearby subways and calling taxis to share rides. The city lifted a shift system for taxis and mobilized 870 school and other public buses.}

This morning's strike apparently involved about 2,000 of the city's 18,000 drivers. Most Koreans work six-day per weeks, including Saturday, but many office workers are on summer vacation now. According to city statistics, as many as 9 million commuters in this fast-growing city use buses on an average work day.

Several hundred bus drivers in the port city of Inchon, 20 miles west of here, also went on strike.

Labor Minister Lee Hun Ki had mediated during a bargaining session Thursday night and yesterday morning that produced an 11 percent wage hike offer that both sides accepted. The union had originally asked for 28 percent, while companies had offered 4.5 percent.

Lee's role represented the government's second such involvement after weeks of saying labor and management should resolve their problems without outside help. More than 1,000 strikes have broken out among South Korea's often low-paid workers since Chun acceded to opposition demands for free elections and other reforms on July 1.

Observers here have said that most of the labor protests of the past weeks have been spontaneous and led by rank-and-file workers. Unions often have been tainted in workers' eyes by years of cooperation with the authoritarian government. The bus drivers proved no exception, responding angrily when union leaders returned to the 89 companies with an offer so far below the drivers' demand.

President Chun's handpicked successor, ruling party chief Roh Tae Woo, has been sounding conciliatory on labor issues, and other party officials recently indicated they might make concessions on another contentious issue, release of political prisoners.

But Chun sounded far less conciliatory this morning.

For example, the president appeared to leave little room for release of prisoners beyond the several hundred who were let out of jail in early July. He said prosecutors believe that those still behind bars "had unmistakably taken part in espionage, were hard-core leaders of leftist organizations which gave aid and comfort to the enemy or had played a leading role in extreme subversive activities."

Opposition leaders and human rights organizations such as Amnesty International have said that a number of prisoners of conscience, not guilty of any crime, remain in jail.

In his speech, Chun also expressed discouragement about the state of Korean youth.

"The way young people dress today and let themselves be carried away by wild music is indicative of their frame of mind," he said.

Chun also said North Korea, which has been negotiating for a role as cohost of the 1988 Summer Olympics scheduled for Seoul, appears only to want "to obstruct the Games completely by employing whatever tactics are necessary." He predicted that North Korea's threat of a Communist bloc boycott will not bear fruit.

"Our armed forces are, of course, maintaining a solid counteroffensive capable of immediately repelling the Communist North in the 1-in-10,000 chance that they launch a military attack against us," he said while discussing the Olympics.

Strikes continued at hundreds of other companies, including Daewoo Shipbuilding and Machinery Co., part of one of the nation's largest conglomerates, and Bayer Pharma Korea Ltd.