The police made 882 arrests in New York City public schools last year, according to a civil liberties group, which said its findings, based on police data, painted a picture of an overly aggressive school security system.

The analysis, by the New York Civil Liberties Union, is the first comprehensive look at the policing activity in the schools since a city law last year began requiring the Police Department to submit quarterly reports to the City Council on arrests, summonses and other interactions that the police have with students in the schools.

The law resulted from complaints by the civil liberties group, which, with a private law firm, has filed a federal lawsuit against the Police Department. The suit challenges what it says is a departmental “practice of wrongfully arresting and using excessive force against children” in the city schools.

Blacks and Latinos made up 95 percent of those arrested, according to the group’s analysis. Those minorities make up 70 percent of the city’s 1.1 million students, according to the Department of Education.

“We’ve now collected a year’s worth of data demonstrating how the impact of heavy-handed policing in city schools falls squarely on the shoulders of black students and young men, who are being subjected to a disproportionate number of arrests at school,” Donna Lieberman, the executive director of the civil liberties group, said in a statement. “If the Bloomberg administration is serious about helping young men of color succeed, then it must address these disparities and focus more resources on educating children, not arresting them.”

The civil liberties group said the figures indicated that the police were “getting involved in noncriminal disciplinary incidents” that would be better handled by a principal or other school official.

Yet the group found that school employees were outnumbered by law enforcement representatives. While there are 5,100 members of the Police Department in the city schools, there are about 3,000 guidance counselors and 1,500 social workers, it said.

School safety officers are, generally, unarmed civilian employees of the Police Department, visible at entrances and elsewhere in schools. When needed, they can call for backup from armed officers in the area.

Paul J. Browne, the Police Department’s chief spokesman, said that while overall crime in the schools was on the decline, the incidents that demanded involvement by police personnel were often more serous than he said the civil liberties group acknowledged.

“They would often like to portray them as simple spats between schoolchildren,” Mr. Browne said. “But, unfortunately, that is not often the case. It can involve serious assaults, with weapons, and including sexual assaults and including serious crimes.”

Mr. Browne criticized any comparisons of crime and a given school’s, or city’s, general population, saying that reported crimes and who commits them is what is relevant.

A spokeswoman for the city’s Department of Education said school safety has improved.

“In the last 10 years, we’ve reduced major crimes committed in schools by 49 percent and violent crime by 45 percent, while still maintaining one of the lowest rates of school-based arrests for any major district in the country,” said the spokeswoman, Marge Feinberg, in a statement. “School safety is important for our students’ success and it’s our goal to preserve a safe learning environment.”

A spokesman for Christine C. Quinn, the City Council speaker, said the Council’s education, public safety and juvenile justice committees were set to hold a public hearing in October on the climates inside the schools, including the issue of school safety.

Among the topics will be the number of arrests made and summonses issued in the schools now that the data from the so-called School Safety Act is in hand, the spokesman said.

Besides tallying arrest figures, the civil liberties group found that 1,666 summonses were issued over the last academic year. It said the most common charge, which was cited in 64 percent of all cases, was disorderly conduct, a “catchall category that can encompass all kinds of typical misbehavior.”