Boston's Roman Catholic Archdiocese will soon close 70 of its 357 parishes in the face of dwindling finances and declining Mass attendance exacerbated by the sexual abuse crisis that began here two years ago.

"Today is not an easy day," said Archbishop Sean P. O'Malley, who leads the nation's fourth-largest Catholic community, in announcing his decision Tuesday. "I wish there were some way that all of these wonderful houses of life and prayer could remain open and alive and full. But there is not."

Citing demographic shifts underway for decades, including the migration of many of Boston's 2.1 million Catholics to the suburbs and a growing shortage of new clergy, O'Malley said that a third of the parishes in the archdiocese are in the red, and that necessary renovations to church buildings would cost more than $100 million in the city of Boston alone. About 130 priests, he said, are older than 70.

Attendance at Mass in the archdiocese, which encompasses much of eastern Massachusetts, has declined by 16 percent since the abuse scandal broke in 2002 and spread across the country.

The parish closings, which will occur by the end of the year, are the latest and most severe instances of a recent trend that has seen Catholic communities across the country shutter churches in neighborhoods that once boasted a different parish for each ethnic group.

The Boston area closed about 47 parishes between 1985 and 2003. The Chicago archdiocese, which says it has about 2.5 million members, has closed 71 churches since 1985, including 10 in 2003. And the diocese of Newark announced last week that as many as 27 churches in northern New Jersey could be forced to close or merge.

The Rev. Gerald P. Fogarty, a historian of the U.S. Catholic Church at the University of Virginia, said of the Boston announcement that he had "never heard of so many churches being closed over such a short period of time," and that demographic changes had dovetailed with the abuse crisis to force a drastic reorganization.

O'Malley said on Tuesday that the money raised by selling off church assets will not be used to fund settlements with abuse victims. The Boston archdiocese reached an $85 million settlement with more than 500 victims last summer, and dozens more have come forward since. It sold more than $100 million worth of real estate in recent months to fund payouts.

During a five-month review period leading up to Tuesday's announcement, 143 churches were candidates for closure. O'Malley decided to close 70 parishes and to form five new ones, for a net loss of 65. Underutilized parishes and those that could be absorbed by neighboring communities were singled out for closure.

"I'm really in a state of shock at this point," said the Rev. Stephen S. Josoma, pastor of St. Susanna Parish in Dedham, a suburb southwest of Boston, who on Tuesday read to about 100 parishioners the letter announcing that his church will close. He vowed to appeal the decision, saying Mass attendance in his church went up by 20 percent in the past two years.

Appeals can be made to the archdiocese and, if rejected, to the Vatican, church officials said.

Voice of the Faithful, a lay Catholic group formed in the Boston suburbs in the wake of the abuse scandal, held a news conference Tuesday to demand that the archdiocese provide more data to show why the closures are necessary, as well as an explanation of how the parishes were selected.

O'Malley, meanwhile, called for unity. "It is not a time to foment divisions but a time to strengthen relationships and build a strong church," he said.

Roman Catholic Archbishop Sean P. O'Malley announces the move to close 70 parishes and to form five new ones.