An emotional campaign launched by dissidents against what they call widespread use of torture by the government has grown in recent weeks following allegations by a labor organizer that a South Korean policeman sexually assaulted her during a station house interrogation two months ago.

The government, which concedes the woman was beaten but not sexually abused, has tried to end further debate on the case.

But many Koreans appear to have latched onto this incident as a means to dramatize their allegations about widespread torture.

Riot police dispersed about 3,000 people who gathered last month for a protest rally on the woman's case at the Myongdong Cathedral and two weeks ago, about 1,000 riot police and plainclothes officers barred entry to Seoul's Anglican cathedral, where another prayer and protest meeting against torture had been scheduled.

Dissidents and human rights activists said the number of torture cases is unknown but that the woman's case is the latest in a series.

Her case is also unusual because Korean women seldom make public accusations of rape or other sexual violence because society typically blames them for such incidents nearly as much as it does their attackers and because their chances of marriage are threatened. But in this incident, the woman sued the policeman, and the case quickly drew wide public interest.

In Washington, the State Department, referring to the woman's case, has noted that four police officials were dismissed in connection with it. "There are credible allegations that the police mistreatment was more severe and harsher than acknowledged," a spokesman said. The department also said, "We find such treatment of prisoners deplorable and appalling."

Dissidents also are questioning circumstances of the deaths in recent months of four men said to have been involved in antigovernment activities. The authorities have ruled that they died by suicide or natural causes.

According to an official at the Human Rights Committee of the Korean National Council of Churches, prisoners are manhandled or beaten so often that many of them consider it routine. Less frequent, but still reported regularly, he said, are more elaborate forms of abuse such as electric shock, dripping of water into prisoners' noses and, for women, sexual abuse or harassment.

Last fall, the government was accused of torturing Kim Kun Tae, an organizer at a dissident group called the Democratic Youth League. Two editors of the major Seoul newspaper Dong-a Ilbo were reported to have been beaten while police questioned them over a broken news embargo. The government dismissed both cases as fabrications.

Dissidents also said the military tortured about 15 persons arrested this spring on charges that included participating in illegal labor activity, making false statements about a joint U.S.-Korean military exercise and taking part in rioting at Inchon.

Critics said police rely on coerced confessions to obtain convictions in many cases, but torture during interrogation is rarely proved beyond a doubt. Reluctance to expose failures of Confucian concepts of moral government or to give communist North Korea material for propaganda are said to reinforce the government's unwillingness to investigate reports of torture. The London-based human rights group Amnesty International has said it knows of many credible reports of torture in South Korea but only two cases in which officials have been prosecuted for it.

The government has dismissed most allegations of torture as fabrications intended to discredit it. Abuse is rare, officials said, and determined efforts are under way to stamp out what does exist. They cited the fact that the sexual assault case was investigated and debated publicly as a sign of progress.

"If that type of thing happened in the past, the police would have tried to put it under a rock," said H.C. Hyun, a former senior official in the Korean Central Intelligence Agency and now a spokesman for President Chun Doo Hwan's ruling Democratic Justice Party.

The government also argues that many of today's dissidents are hardened revolutionaries who, while in custody, provoke officers by shouting obscenities, destroying government property and, in at least one case, throwing excrement.

The accuser in the sexual assault case is a 22-year-old radical labor organizer who formerly attended the elite Seoul National University. She alleged that during interrogations at a police station in Puchon, west of Seoul, on June 6 and 7, a policeman forced her to remove most of her clothes, beat her, attempted to have oral sex with her and committed other acts of sexual violence. During the ordeal, he repeatedly demanded to know the names of other dissidents, she said.

A committee of nine lawyers formed by the opposition to defend the woman interviewed her in jail and issued a report amplifying her claims. The report circulated in churches and dissident offices, since South Korea's closely supervised newspapers did not print full details.

Under pressure, the government conducted an investigation. It announced afterward that it had found that the policeman had forced her to remove her jacket in order to humiliate her, had hit her on the breast six or eight times during interrogation and had used abusive language.

This, however, did not constitute sexual abuse, it said. Her charges were fabrications aimed at "damaging the prestige of law enforcement agencies and abetting and escalating revolutionary antiestablishment struggles," it said in a formal statement. It also accused her and fellow activists of leading "morally decadent private lives."

The policeman was fired, but prosecutors said they would not indict him because he had a good record until this case and was repentant. The woman remains in jail on the original charge of stealing a resident registration card with the intent of using it to conceal her student background and get a job at a factory.

Dissidents said prosecutors found out the true story but got orders from above to back off.

"The government doesn't want to punish him but protects him," said Kim Dae Jung, an opposition leader. The government is adamant that the full story is out.