Sitdown strikes, walk-outs and other labor protests, some of them violent, are spreading across South Korea in a wave of worker uprisings that were never tolerated during the reign of the late president Park Chung Hee.

At least 25 companies have been subjected to strikes or other actions demanding higher wages and the ouster of pro-management union leaders. Representatives of both labor and business groups call the extent of the actions unprecedented.

Workers in several industries have sat down on shop floors, occupied managers' offices, smashed furniture, and on two occasions fought violently with police.

A demand for higher wages in the face of soaring inflation is one reason for the uprisings. Yet both strikers and businessmen say the major reason is that, for the first time in years, the government is not intervening on management's behalf in labor disputes -- in effect, permitting technically illegal strikes to go on unhampered.

Two disputes have been marked by widespread violence. In the southern port city of Pusan, about 1,000 steelworkers clashed last night with local police during a protest demanding a 40 percent wage increase. Eleven policemen and one steelworker were injured.

In the most serious confrontation, coal miners last week took over the central city of Sabuk, attacked a police station, killed a policeman, and demolished several houses. They were trying to oust their union president who had accepted a 20 percent company wage increase instead of a figure twice that much being sought by the rank and file.

Other plant rebellions have been settled without serious violence, largely because employers have granted big wage increases to avoid more trouble.

Here in Seoul, for example, 980 workers at the II-Shin Steel Co. sat on the shop floor for two days last weekend chanting slogans and shouting their demands.

Management surrendered and by Monday afternoon workers had posted at the plant gate a list of their victories: doubled bonuses, an average wage increase of 25 percent and the ousting of the union president deemed subservient to the management.

The wave of unrest has shocked businessmen and government officials. Coming on the heels of widespread campus demonstrations by students, it has triggered fears of a military crackdown and further trouble.But neither the civilian government nor the martial law command has stepped in.

Strikes are illegal under South Korea's national security law and were rarely attempted during the late president Park's long rule. Occasional protest actions were frequently followed by harassment by the South Korean Central Intelligence Agency. Persons advocating strong trade union activities were often arrested.

But the interim civilian government that followed Park's assassination last October has decided to let the disputes this year run their course. "The government seems to have an unstated policy that these [strikes] are alright so long as they do not disturb the social order," said one business leader.

In interviews yesterday, II-Shin workers made it clear that their sitdown strike was staged because they knew the government would not intervene. They said in the past government pressure and pro-government union leaders made such actions impossible. "The pressure is lifted now," one of them said. None would permit his name to be printed, however, because retaliation by the government or management is still feared.

Airing a complaint typical of many current strikes, the II-Shin employes said the ouster of a despised union president was a major goal. They maintained he was chosen in a rigged election managed by the government and employers. II-Shin's management agreed to arrange his resignation, they said.

About one out of five industrial workers belongs to unions, almost all of which had been subjected to tight government control in Park's days. The KCIA, before his assassination, wielded great influence over the Korean Federation of Trade Unions and handpicked many of its leaders. In one ironic sidelight of this week's actions, the federation's offices were invaded by two dozen women hunger-strikers who pulled a sit-down in the president's office.

Substantial wage increases already have been promised this spring. Reports tabulated by the Urban Industrial Mission, a church-sponsored labor group, show many factories have been forced to reduce working days from 12 to eight hours and to grant sizable pay increases

According to Hwang Chung-hyun, execative director of the Korean Employers Association, the average wage increase so far has been about 25 percent, despite a government guideline seeking to limit them to about 15 percent.

Hwang, who said the scale of protests is unprecedented, thinks the fear of inflation is driving workers to make exorbitant demands. "There is one machinery plant where they're asking for 50 percent," he said. "How can anybody pay that."

Business leaders are shocked and angered by the unrest but agree employers will try to meet most demands unless the government intervenes.

The labor movement is "spreading rapidly and won't reach its peak for months," said one executive who asked not to be identified in print. "It is just the beginning."

The businessman thinks the new freedom from government intervention, not merely a desire for higher wages, is the major factor now. "It is a reflection of the tight control that existed over many years," he said. "It just cannot be coped with by rational discussion."

South Korea built its economic boom of the 1970s on low-wage industries, especially textiles, shoes, and electronics. Wages were kept low by a policy of management-government pressure to assure the country's products would remain competitive with those from other growing Asian nations.