SEOUL, JAN. 30 -- The South Korean Supreme Court has ruled that a policeman accused of sexually assaulting and torturing a young labor activist was wrongly freed two years ago and must stand trial.

The policeman was fired but not prosecuted in 1986 despite strong evidence against him in a case that the U.S. State Department then called "deplorable and appalling." The alleged victim was Kwon In Suk, then 22, who became an important symbol for the political opposition here.

The decision by a three-judge panel yesterday represents the second time since last month's presidential election that a widely publicized torture case has been reopened. Earlier this month, a former national police chief was arrested and charged with attempting to cover up the torture death of a politically active student one year ago.

The two actions have raised hopes that the legal system may act more independently in cases involving human rights and political dissent than it has in the past. Roh Tae Woo, who won the Dec. 16 presidential election, is scheduled to succeed President Chun Doo Hwan on Feb. 25 and has promised a more democratic regime.

But human rights lawyers and opposition politicians here cautioned that many problems remain. They have charged that higher level officials are being protected in both torture cases and that many political dissidents remain in prison.

Kwon was arrested in 1986 in Puchon, an industrial town between Seoul and Inchon, and charged with falsifying her identity documents. She allegedly had concealed her university background so she could be hired as a blue-collar worker and help organize the labor movement.

During the night of June 6 and on June 7, a policeman named Mun Kwi Dong stripped Kwon's clothes, forced her to commit sodomy and humiliated her, according to her lawyers. According to one report, she subsequently attempted suicide.

Fellow inmates reported the assault to church workers, who publicized the case and demanded an investigation. The government concluded that the policeman had forced Kwon to remove her jacket and had struck her on her breasts but that nothing he did constituted abuse.

Government investigators also said the charges were aimed at "damaging the prestige of law enforcement agencies." Mun was fired but not prosecuted because, officials said, he had a good prior record and was repentant.

Kwon was sentenced to 18 months in jail. She was freed in an amnesty last July.

The Korean Bar Association, after its own investigation, said, "There is not a bit of doubt in the allegation by the coed that she was sexually tortured," the lawyers concluded.

The U.S. human rights organization Asia Watch also noted that "it is unlikely that any female detainee would willingly fabricate charges of this sort, given the profound stigma within South Korean society associated with such a revelation."

South Korea's top judges, who were appointed by Chun and have rarely challenged the executive branch, ruled yesterday that the policeman's release was illegal.

"Mun imposed both physical and mental pain on the woman defendant by sexually abusing her, an offense which was unpardonable," the presiding judge said.

The appeal was filed by 166 lawyers on Kwon's behalf in November 1986. One lawyer, Cho Yung Nae, said five other police officers, including the station chief, had condoned the torture or helped conceal it afterward and should be tried.

Kwon said those responsible for freeing Mun should be identified. "How government power helped in the cover-up should be disclosed," she said.

The earlier torture case involved Park Chong Chul, a student activist whose name also became a rallying cry for protesters after he died while being tortured by police last year. A former national police chief, Kang Min Chang, is in jail awaiting trial for attempting to conceal the cause of Park's death.Special correspondent Young Ho Lee contributed to this report.