DESEGREGATION of the Catholic schools in Washington, beginning in 1949, was one of the most influential acts of moral leadership in this city's history. Cardinal Patrick A. O'Boyle, who as archbishop presided over it, would have attributed it all to the teaching of his church on race and justice. But most other people think that Cardinal O'Boyle himself, a talented administrator with strong convictions, had a lot to do with it.

When he began dismantling the rules of racial separation in the church's schools, he knew that the federal courts were slowly moving toward a decision on the public schools. He wanted to demonstrate to the judges, and to the country, that it could be accomplished smoothly, safely and peacefully. Because he and the people working with him went to some lengths to keep it out of the newspapers, it also happened quietly.

In 1949, desegregating a school system was a very daring, not to say dangerous, endeavor. That was a time when Congress was full of men, some with great power, who spoke frequently on the subject of how God meant the two races to live, and their views were very different from Cardinal O'Boyle's. Washington was a city of almost total racial segregation, enforced by law and tradition. The cardinal received many warnings that he would do grave damage both to his church and to his own standing if he tried to contravene this fundamental social convention. But he thought it unjust and un-Christian, and that was that.

In 1963, he was in the middle of the great civil rights march here and delivered one of the prayers that memorable day at the Lincoln Memorial. Later in the 1960s the cardinal, having been trained as a social worker in New York during the Depression, saw to it that the Catholic schools here participated fully in the programs that Lyndon Johnson's war on poverty offered children from poor families.

The migration of middle-class families to the suburbs left many inner-city parochial schools destitute of financial support. Cardinal O'Boyle used diocesan money to keep them open and organized visits between the city and the suburbs to open lines of communication at the personal and parish levels.

He led a rich life of service to his church, and perhaps it was his work within the church that meant most to him. But the Catholic archbishop of Washington is always a civic leader of great authority. Cardinal O'Boyle, who died Monday at the age of 91, used that authority strongly and well at a crucial time in this city's life.