The condominium board of a Washington Heights building is facing a discrimination lawsuit on behalf of five mentally retarded adults who want to move in.

The lawsuit, filed recently in federal court in Manhattan, is the latest chapter in Margaret Puddington’s effort to find a suitable home for her son and four of his friends.

Mark Puddington, 26, and his intended roommates are mentally retarded to varying degrees. Although Mr. Puddington is relatively young, Ms. Puddington, 65, wants to move him into an apartment that will be his home into old age. She needs a place with no stairs, which leaves out brownstones.

After reviewing about 200 properties, Ms. Puddington said in a telephone interview this week, she set her sights on two neighboring units in the Bennett, a Washington Heights condominium.

When the condominium board and property managers of the West 187th Street building learned that their proposed neighbors were mentally retarded, they balked at the $1.3 million deal, Ms. Puddington said.

A federal judge in Lower Manhattan, Alvin Hellerstein, is hearing a federal Fair Housing Act lawsuit against the Bennett, and will decide whether the group will be permitted to purchase the units.

The lawsuit on behalf of the five adults is being brought by the Young Adult Institute, a nonprofit organization that provides services, including staffed group homes, to the mentally retarded across New York City. It is the first time YAI has filed a housing discrimination lawsuit, an associate executive editor of the organization, Thomas Dern, said.

The president of the condominium board, Barry Siegel, declined to comment when reached by phone, citing the pending litigation.

Local community boards do have a right to block group homes such as the one YAI and Ms. Puddington are proposing. But they can only do so when a neighborhood is already “so saturated with facilities of this type” that one more will change the character of the area, the chairman of the housing and human services committee of Community Board 12, Julio Rodriguez, said in a telephone interview. Mr. Rodriguez said the community board approved YAI’s application to purchase real estate at the Bennett last year.

Still, according to the plaintiff’s legal papers, property managers from the Bennett asked YAI whether the property values of its condominiums would be affected by their proximity to the units in which the five mentally retarded adults lived, according to a the legal complaint.

“This is blatant discrimination and it’s against the law,” Ms. Puddington said. “Our children are just as worthy as non-disabled children to live in a decent place.”

The group of five includes three men and two women. Three still live with their parents, and two already live in other group settings. In preparation for the move, the group has taken about four weekend trips together, Ms. Puddington said.

Mr. Puddington, who communicates in limited sign language, is aware that he was supposed to move by now, Ms. Puddington said. But she said she did not try to explain to him why he has not.