Detectives in Northern Ireland beat and kick suspected terrorists to extract confessions, according to a report Amnesty International is scheduled to release next week.

The abuse is frequently directed at men and women against whom no charges are lodged, and is so frequent that Britain should conduct a public inquiry into it, the report says.

The 70-page document, a copy of which has been obtained by The Washington Post, says that medical and psychiatric evidence supports the claims of victims that they have been struck in the head, body and genitals, thrown against the walls, threatened with rape and subjected to relentless humiliation.

The Amnesty investigating team included two unnamed Danish doctors who examined medical reports of 39 arrested persons and conducted their own examination of five. The Amnesty doctors discovered organic brain damage in two of these cases, both of whom are ultimately released by the police without charge.

The report by the humanitarian organization, winner of the Nobel Peace Prize last year, is likely to rub British sensibilities raw. There is a wide spread belief here that police abuse is a problem in dictatorships or the United States and that British police - even in tormented Ulster - play fair.

To rub it in, Amnesty's director, Martin Ennals, is a brother of David Ennals, a Cabinet minister for health in Prime Minister James Callaghan's government.

Officials here declined to comment on the report until it was publicly released. They indicated, however, that they would examine every Amnesty complaint if the organization would release the names of those who made them.

The surgery by the London-based organization asserts that plain-clothes officers of the Royal Ulster Constabulary -- not the uniformed police who patrol the streets -- are typically the assailants. The Amnesty team did not look into the charges that British soldiers, who also make arrests in Ulster, frequently maltreat their prisoners.

The report is likely to touch off heated controversy when it is released here Tuesday. The British Government's Minister for Northern Ireland, Roy Mason, frequently boasts that he is supressing bombings and shootings in Ulster by convicting terrorists in the courts.

The Ulster conviction rate is high. About 94 of every 100 persons charged is found guilty by the one-judge, nojury courts especially set up in Northern Ireland. There is also the fact that 70 to 90 percent of these convictions rest wholly or mainly on the accused's own admission, according to another study.

If Amnesty is correct, Mason appears to be open to the charge that his court structure rests heavily on the maltreatment of suspects. To be sure, witnesses to terrorist crimes are hard to find in Ulster, either because they fear retaliation or because they sympathize with the terrorists. The document asserts that the Mason system has been strengthened by police practices which isolate suspects from lawyers for several days and by little-noticed changes in British law that no longer bar confessions obtained through fear of oppression.

Most of the cases examined by the Amnesty team are Catholic because the Catholic Provisional Irish Republician Army accounts for the bulk of terror in Ulster. Some Protestants are included, however, presumably suspected terrorists from IRA counterparts like the Ulster Defense Association.

The report does not name any of its alleged victims, but describes the complaints and medical history of several in great detail.

Case number three is a male who was released without charge about 4 1/2 days. He said he was subjected to "prolonged oppressive questioning ... threats (of being killed) ... beatings (hit in face and stomach, kicked on the legs and buttocks ... humiliation (soiled underpants were placed over his head, humiliating remarks were made about his religious beliefs.)"

The Amnesty doctors who examined him several months after his arrest "found a positive test for cerebral asthenopia which suggests that he is suffering from some degree of organic brain damage."

The report said, "there is consistency between allegations of maltreatment and the attached medical reports ... and the detailed examinations, which enabled the medical delegate [Amnesty doctors] to assess the symptoms described and detect residual signs, strongly corroborates the case that maltreatment took place."

Case number 12 was a woman held three days and also freed without charge. She said she was threatened with rape and electric shock, that her child would be taken from her. Her skirt were lifted, one of her interrogators "forced her to stand against the wall and then hit the wall next to her head with his fist."

Examining her several weeks later, the Amnesty doctors found her still suffering from symptoms she first complained of when she was freed - irritability, talkativeness, erratic behaviour, fatique, depression and anxiety. They described her as "moderately depressed and concluded that their examination" strongly corroborates the case that maltreatment took place."

Amnesty could not determine the extent of the practice. It did discover that more than three of every four complaints examined came from police holding center in East Belfast.