By DAVID GONZALES


Behind the red-brick walls encircling the Convent of Mercy in Brooklyn generations of nuns have taught the illiterate, sheltered the homeless and raised orphans. They are known as the Walking Sisters, ministering in the community as well as inside their convent.

Now, after 146 years, it is time for the small band of sisters, most of them retired, to walk away from the convent. The leadership of their order, the Sisters of Mercy, decided to shutter the place and scatter the 38 sisters to other homes and nursing facilities after realizing it would cost more than $20 million to fix serious structural and accessibility problems in the fortresslike building.

This has been a season of heartbreak and anger for these women, who thought the motherhouse would be their last home and the sisters their constant companions. Now they, the rescuers of lost children, feel like orphans themselves.

“It kind of hurts in a lot of ways,’’said Sister Francene Horan, who came to the motherhouse in 1950 to teach kindergarten.“A building is one thing. This is a home, the place you knew would give you a place to stay. It’s like saying your parents died and you don’t have a home anymore.’’

In a ritual that was unthinkable a year ago, they gather regularly as their numbers dwindle to bid goodbye to one another, and to an entire way of life.

The Sisters of Mercy, known as the Walking Sisters because working outside the convent was unusual for nuns in the 19th century, have been in Brooklyn since 1855, when five young nuns from Manhattan answered Bishop John Loughlin’s call to work with the poor and sick. As the nuns’ work grew , they moved in 1862 to their present convent. Thousands of children came to live with the sisters over the decades.

Mary Margaret Mc- Murray was almost 6 years old when she and her sister arrived at the orphanage after their parents died of influenza in 1917. She stayed until she graduated from high school and took a job as a secretary.

“The convent was so big,’’said Ms.McMurray, now 97.“And there were so many children there. I had a lot of company. But it was very pleasant.’’

Changes in social welfare policies in the 1970s led the order to open group homes, encourage adoption or foster care, and expand services to the homeless and developmentally disabled. Fewer women were entering the order, while the remaining sisters grew older. The convent became their retirement home.

The order’s leadership realized in the last few years that the old building presented too many obstacles for older women. An engineering study in February recommended extensive exterior renovations, removal of asbestos and rebuilding the foundation.

Sister Christine McCann, the president for the region that includes the convent, said the m oney needed for repairs could be better used to finance social and educational work by the order, which still has about 4,000 nuns in the United States. Sister McCann knows the news was hard to break, and understands the anger that greeted it.

“It’s difficult when any community has to make these decisions that affect the lives of so many people,’’she said.“But I’m awed by the response of the sisters who live here. They have been honest with their feelings, fine one minute and not so fine the next. But their faith is constant. To live as a Sister of Mercy is to take the steps they take with courage.”