SEOUL -- Splashed across South Korea's front pages, the charge was so shocking that the country's fledgling stock market tumbled further in one day than ever before.

A research foundation with close ties to President Chun Doo Hwan, the opposition alleged, had colluded with his government to manipulate the market for huge, illegal profits.

Almost everyone had heard such rumors. What stunned the stock exchange, and much of the public, was to hear the unsubstantiated charges made openly, and to see them displayed so prominently in Korea's leading dailies.

In a nation where even oblique criticism of Chun has been off limits for the tightly controlled press, the Ilhae Foundation story was an astonishing turnabout, a sign of how much has changed since Chun promised democracy three months ago. But the episode also illustrated that not all the fetters have come off. The articles about the foundation barely mentioned Chun, leaving the most titillating elements of the story to the medium that has flourished most since Chun's military coup seven years ago: word of mouth.

A freer press appears to be emerging in South Korea, but fitfully. Blacklisted journalists have reappeared, long-stifled stories have aired, former nonpersons appear once more on television screens.

Yet some taboos remain inviolable, by government fiat in some cases and by ingrained habits of self-restraint in others. Most notably, the official line is still largely followed when reporting on North Korea or Chun and his family.

Control of the press was one of Chun's top priorities when he and his fellow generals took over seven years ago. The government shut some newspapers and television stations, took over others and had 700 independent-minded journalists fired.

But early this summer, widespread street demonstrations persuaded Chun to accede to opposition demands for direct presidential elections and other reforms, including a freer press. Since then, the stirrings of the emboldened media have been remarkable.

Song Kun Ho was managing editor of one of Korea's largest dailies when he resigned to protest interference from an earlier government in 1975. He spent a year in jail after Chun took power and then began publishing Mal (Words), an underground newsletter featuring stories that his old newspaper would not print.

Until this summer, editors of Mal would be rounded up and jailed after every issue, and distribution was strictly "under the jacket," delivered covertly by young students risking jail terms. But the September issue, reporting on widespread labor unrest more sympathetically than have the mainstream newspapers, was sold openly, if still without a license, and no editor went to jail.

Now Song, along with some journalists fired in 1980, is raising money for what he says will be Korea's first unbiased daily, scheduled to debut next March.

Editors and reporters of the mainstream press are living in what one editor called a "completely new world." The government's propaganda officials no longer make their daily rounds, instructing which news should be ignored and which should be played up.

Newspapers once again may post reporters in the provinces instead of relying on the government wire service, and the government no longer controls how many pages they may publish each day. They still print articles about Chun receiving thank-you notes from Pope John Paul II and President Reagan for the commemorative Olympic coins that Chun sent them, but such articles appear inside, not on the front page. In contrast, news of opposition leader Kim Dae Jung, whose photograph did not appear for seven years, has become routine on front pages.

Still, critics of the press remain. Newspapers give big play to infighting in the opposition party, they point out, but never mention tensions between Chun and ruling party candidate Roh Tae Woo.

The ruling and opposition parties now are drafting a new press law intended to insulate newspapers and television somewhat from government influence. The ultimate test may be how, and whether, they cover the president and his family, about whose business dealings rumors have swirled for years.

The press stepped gingerly when the Ilhae Foundation story broke. It did not pursue allegations that Chun created the foundation, named it after his own pen name and dunned major companies to support it as a sinecure for his retirement days.