Mark Davidson lifted his striped sports shirt to reveal an abdomen and back lined with small brown spots of burned skin. "I was screaming and pleading for them to stop," he said in an interview. "I asked to call my mother.

"They told me, 'This ain't TV, nigger.' "

The incident, which the Queens district attorney has labeled a case of "medieval torture," has raised questions about the extent of police brutality in the nation's largest city. Davidson is one of four blacks who, prosecutors say, were tortured with electric stun guns by five Queens police officers after being arrested on minor drug charges.

The indictment of the five officers last week -- coupled with more than a dozen highly publicized incidents of police brutality and misconduct here in recent months -- raised again the polarizing issues of race and crime just as the case of Bernhard Hugo Goetz, the subway "vigilante," was fading.

Nationwide, police brutality has been a sporadic issue in the years since the 1960s, when some blamed it for sparking race riots. While no hard statistics are available, experts say new guidelines and more awareness of the civil rights of suspects have resulted in fewer deaths and less overt police brutality. Nonetheless, brutality still crops up as a major problem across the country.

In San Francisco, one police officer pleaded guilty recently and another was convicted of felonious assault after dragging a homosexual man off a city bus, beating him and crying, "Die, faggot!" The incident was the latest in a rash of offenses beginning in April 1984 when two San Francisco vice-squad members paid a prostitute $55 to have oral sex with a police recruit handcuffed to a chair at a party. City supervisors have recommended that the civilian police commission be replaced or the police chief fired.

In Winnemucca, Nev., the 20-member police force has been hit with civil rights lawsuits by 84 victims of alleged brutality. Officers have admitted driving hobos to the city dump, taking their shoes off and pushing them over the edge into glass and garbage.

"We've made progress," since the 1960s, said Benjamin L. Hooks, executive director of the NAACP. "But there is, in America in 1985, police abuse of authority . . . . There may be a trend toward looking more closely at it" by the news media and by politicians, he said.

Amitai Schwartz, staff counsel with the American Civil Liberties Union of Northern California, says the problem is no worse than it ever was, "but there has been more public attention focused on it and standards for police behavior are getting higher."

In 1983, Rep. John Conyers Jr. (D-Mich.), armed with hundreds of complaints from black citizens that New York was ignoring reports of police violence, held highly publicized hearings here. A report issued by his subcommittee on criminal justice concluded that "racism appears to be a major factor in New York police community relations." In an interview, Conyers said, "It seems like we have an epidemic of police violence that is surfacing." But he said he won't hold new hearings because, unlike in 1983, officials are responding to the crisis.

Mayor Edward I. Koch appointed a black police chief after the Conyers hearings in 1983 and, in the wake of the recent torture incidents, has called on Attorney General Edwin Meese III to investigate the matter and to prosecute the officers for alleged civil rights abuses. The highly publicized brutality incidents could exacerbate Koch's unpopularity among blacks and Hispanics in his reelection campaign this summer.

City Council President Carol Bellamy, Koch's principal challenger, has called for appointment of an independent investigative commission similar to the Knapp Commission, which exposed corruption in the city's police force in the 1970s.

Citizen complaints here have risen by more than 2,000 to an annual total of 6,689 in 1984. More than half involved allegations of excessive force. Last year, 81 police officers here were arrested on criminal offenses -- up 45 percent from 1983. In the first four months of this year, 22 were arrested. Koch says, however, that police brutality in the 26,000 member force -- more than twice as large as any other in the nation -- "is not systemic. These cases are individual in nature."

In the wake of the torture allegations, Police Chief Benjamin Ward, saying he felt "personal shame and disgrace," transferred the entire command of 18 top-ranking officers out of the 106th Precinct, where the incidents occurred, and forced the early retirement of four of the city's highest commanders, including the department's third-ranking official.

He also transferred investigative authority from the Civilian Complaint Review Board, widely criticized as ineffectual, to the Internal Affairs Division, set up in the wake of the corruption cases of the 1970s.

However, attorney Richard Emery of the New York Civil Liberties Union said the chief may be part of the problem, adding that internal reports revealed that Ward had used his office as corrections commissioner for "late-night and weekend meetings with a female guest," had used city employes to help him repair his boat, and had appeared to be drunk during a Patrolmen's Benevolent Association Convention.

In the case of Mark Davidson, 18, a high school student who had never been arrested, the Queens medical examiner found 49 electrical burns on his stomach, back, buttocks and thighs the day after he was arraigned on charges of selling a packet of marijuana to an undercover agent for $10.

Davidson was standing on a street corner on April 16 near his house in the integrated working-class neighborhood of South Ozone Park, near Kennedy Airport, when six policemen jumped out of a green station wagon and seized him, taking him to the 106th Precinct.

Son of a disabled post office employe and an airline food-services worker, Davidson related the incident in a calm monotone in the office of his attorney, Marvyn Kornberg. "It was a normal day," he said. He had gone to get a haircut, to an appointment with the eye doctor after school and then to a friend's house.

Two policemen questioned him at the station, demanding "Where is the $10?" after finding only 26 cents in his pocket, he said. "One of them punched me in the eye and rammed my head into the wall. Another one threw me on the table." Finally, he said, they burned him repeatedly with the stun gun, a walkie-talkie-shaped device that emits a blue 50-volt charge that travels through clothing and burns the skin without marking the clothes. After a half-hour the officers allegedly held the device to his groin; then, he says, he falsely confessed.

After the allegations became public three other men -- all black, including a 24-year-old janitor, a 31-year-old cab driver and a 17-year-old student -- came forward with allegations that officers at the 106th Precinct -- labeled "Torture Precinct" by the tabloids -- had burned them with a stun gun.

The five officers have pleaded not guilty.