Apologies have been made for slavery, sexual abuse, anti-Semitism, and mistreatment of women and gays.
The cardinal himself stood before the racially diverse congregation to make a confession.
"Among the sad facts of our own early history is that religious communities, Catholic laity and even our first bishop had slaves," Cardinal William Keeler said from the pulpit of the Basilica of the National Shrine of the Assumption of the Blessed Virgin Mary.
"The slave of Bishop (John) Carroll was set free in the end, but the Catholic slaves and free blacks were required, when they came to the Basilica in the early days, to take their places in the galleries in the rear of the church."
Keeler asked forgiveness from fellow Catholics for the church's legacy of slavery and segregation, calling racism "a spiritual malady that gnawed at the moral fiber of our nation, our community and our church."
Following the lead of Pope John Paul II _ who in March asked forgiveness from God for wrongs committed by the Catholic Church over the centuries, including those inflicted on Jews, women and minorities _ church leaders around the world have been delivering messages of regret and reconciliation this year.
It's all part of the church's observance of a Jubilee year, meant to coincide with the 2,000th anniversary of the birth of Christ. Taken from a Jewish tradition, jubilee years were marked by acts of grace such as forgiving debts and releasing prisoners.
John Paul built on that tradition with his apology and calls to renew faith, reduce Third World debt and abolish capital punishment.
At what he called an "extraordinary service," Keeler tailored his message to the history of Maryland's church, specifically its imperfect record on race relations. Baltimore was the first Catholic archdiocese in the United States.
Earlier, Cardinal Roger Mahony of Los Angeles and Cardinal Bernard Law of Boston apologized on the church's behalf for sexual abuse, racism, anti-Semitism and mistreatment of women and homosexuals.
"We turn to God and acknowledge our sins, the sins which obscure the holiness of the church today and the sins which have obscured that holiness in years past," Law said in July at Encuentro 2000, a national gathering of Catholics in Los Angeles.
Bishops in Colorado and Oakland, Calif., similarly apologized, and Santa Fe, N.M., Archbishop Michael Sheehan sought pardon from American Indians, among others, for the church's uneven record as missionaries during colonization.
Even three orders of nuns in Bardstown, Ky., apologized for the use of slave labor by their predecessors.
"What I see is, in each setting, there is a different set of problems, a different set of challenges," Keeler said before his service. "We're responding to the challenges in this setting."
In the past, the church has deflected responsibility by simply acknowledging that its members are sinners, said the Rev. Thomas Reese, editor of America, a weekly magazine published by the Jesuits.
"In church terms, it's a pretty big deal," Reese said. "What's different this year is we're doing this as a community, as an institution, and that's something that's hard for institutions to do."
The church itself has long been a minority in America. Government leaders and the elite rarely were Catholics, so the church here "couldn't do as much damage," Reese said.
Still, the church admits it did not lead the way in social justice at times when slavery, segregation and gender inequality were sanctioned by the government, he said.
"When you go to confession, you confess your sins. You don't try to make excuses," Reese said.
Lawrence Cunningham, a theology professor at the University of Notre Dame, said such apologies are uncommon throughout history. Yet popes and, more typically, saints in the Middle Ages "would talk about faults in the church and the need to correct them," he said.
The cultivating of "interreligious and ecumenical relationships" in the 20th century paved the way for the collective introspection that has helped the church confront its past, Cunningham said.
"I think there has arisen in the church, at the intellectual and hierarchical levels, a greater historical conscience," he said.
Although some say the apologies are too little, too late, Annette Kane, executive director of the Washington-based National Council of Catholic Women, welcomed them.
"It's not just a matter of saying, "Sorry,' but saying, "We're going to do business a different way.' " She wants to see women given greater roles in the church.
Hilbert Stanley, executive director of the Baltimore-based National Black Catholic Congress, said the church has made "some progress" in the past 30 years, but he doesn't expect racism to be eliminated overnight.
The apologies were positive steps, he said, as were the canonization of Josephine Bakhita, from Sudan, as a saint in October and the appointment of Edward Braxton, who is black, as bishop of Lake Charles, La.
But those big changes are easier to make than subtler ones, such as changing the attitudes of local parishioners.
"There are still some pockets in this diocese and in the country where blacks are not welcome," he said. "When you go to church, you ought to feel comfortable when you're there."