Political leaders and black ministers today joined to denounce the hostile racial climate that police say they believe triggered the shooting of a black high school football player during a game last Friday in a white neighborhood.

The ministers called the session with leaders from business, government and the media to urge cooperation in defusing rapidly escalating racial problems.

Boston's schools, a barometer of racial hostility since court-ordered desegregation was begun here five years ago, remained calm today as high-level talks continued on heading off the recent violence.

Three white teen-agers from Charlestown, home of a strident antibusing group, "The Powder Keg," were arraigned today in District Court on charges of assault and battery with a dangerous weapon.

Darryl Williams, 15, remains in critical but stable condition at Boston City Hospital. He is paralyzed from the neck down with a .22-cal. bullet near his spine.

Police Commissioner Joseph Jordan, who said the shooting "surpasses any kind of problem we've ever had," ordered additional security today to ensure the safety of the city's 66,500 public school students.

Calling the shooting "only the latest and the worst," Patricia Corcoran of the citywide Parents Advisory Council, a biracial board established by the federal court to monitor school desegregation, called for a noon rally Wednesday near City Hall.

Meanwhile, state Sens. William Owens of Boston's mostly black Mattapan section and Francis D. Doris, who represents Charlestown, filed legislation today that would defray Williams' medical and educational expenses.

The bill is also backed by Mayor Kevin H. White, who called the shooting "an ugly, vicious and apparently racially motivated attack on a boy . . . and on the sanity of this city."

Even as final preparations were being made last weekend for the visit of Pope John Paul II to this city, White was meeting with the city's black leaders in an effort to quell tensions.

"The pope's visit has been awesome in its ability to inspire Bostonians of every creed and color," the mayor said. "We must build on a climate of calm and optimism generated by the papal visit to rededicate ourselves to making Boston a city of peace and safety for all its residents."

During Monday's papal visit, about 1,800 members of the black community marched on the cathedral where John Paul was to protest what they said was the church's silence on last week's shooting.

"We suggest that Humberto Cardinal Medeiros begin to take some moral and spiritual leadership in this city," Owens said. "The pope shouldn't be accountable for what happens in this city -- city leaders should."

A letter signed by hundreds of Charlestown residents and delivered to William's mother by two priests expressed the white neighborhood's "shock and sense of disgrace that we feel over the mindless, savage shooting . . . ," and asked for forgiveness for "all the racist madness that consumes the hearts of a few who bring dishonor" to all the people of Boston.

Meanwhile, the Rev. Michael Haynes, a minister and black community leader, called the mood of his parishioners "anxious, angry, hurt, tense, and there is a boiling that could boil over. People are in a rage."

He said the incident at Charlestown High School "underscores the fact that there is a terrible hostility against blacks in Charlestown."