The 2400 block of Ontario Road NW is a friendly stretch where residents sit out on their stoops or tend small front gardens in the evening, but acceptance has come slowly for one household in the Adams-Morgan neighborhood.

The house, at 2474 Ontario Rd., is operated by the Community of the Ark (COTA), a Washington affiliate of the international group L'Arche, which forms group homes for mentally retarded adults.

"Little by little, people are starting to say, 'Hey, it's just like another family,' " said COTA director Kathy Bruner, 29.

On Sunday, L'Arche founder Jean Vanier concluded a "Faith and Sharing" retreat held in Washington over the weekend with an address at the Shrine of the Immaculate Conception.

Approximately 700 people packed the pews in the church crypt to hear the tall, white-haired Vanier anecdotally articulate the L'Arche philosophy. He told, for example, of bathing a severely handicapped child in warm water so "that he could gradually discover he was precious" and of meeting a neglected, handicapped child who, upon encountering a new person, would "climb up on that person's leg and just hug and hug and hug."

"The secret of Jesus is to go down the ladder and share with those who have less, and build with them, celebrate with them, rejoice with them," Vanier said, explaining the motivation behind the founding of L'Arche 21 years ago.

After joining the Canadian Navy at age 13, and later teaching philosophy at St. Michael's University in Toronto, the Canadian-born Vanier visited a home for 30 mentally handicapped men in France called the Val Fleuri. That led him to explore the institutional lives of mentally handicapped persons in hospitals and asylums.

"They would get up in the morning; they did nothing all day . . . . You just can't imagine the pain. Some say that those who have mental difficulties do not suffer . . . my experience was exactly the opposite."

L'Arche began when Vanier invited two Val Fleuri residents to visit him outside of Paris for a holiday. After a month, they chose to stay indefinitely. There are now 70 L'Arche communities in 18 countries around the world.

The Adams-Morgan household and the Community of the Ark were established in October 1983 with private donations and $50,000 from the Joseph P. Kennedy Memorial Foundation. COTA extensively renovated the house, which they leased on a long-term basis from the ecumenical Church of the Saviour.

Four mentally retarded adults, each of whom holds a job outside of the home, and four COTA staff people now live there.

"It Adams-Morgan is such a transient neighborhood that people were glad to see that we'd come here and were fixing up the house to make that our permanent home," said director Bruner, who previously worked in a L'Arche home in Erie, Pa. Residents came from Forest Haven, the District's facility in Laurel for the mentally handicapped, and from shelters for the homeless.

"When people found out that L'Arche was coming here, we received hundreds and hundreds of applications," Bruner said. "We were anxious to welcome people from the immediate neighborhood and people who were most in need."

A piano, guitars, pipes and smoking tobacco fill the inviting living room of the house, along with an unfinished puzzle, and Tucky, the household's rambunctious black puppy. Bruner said residents like to sit on a carpeted window seat that faces Ontario Road or on the stoop outside and "enjoy the world."

"The community here is remarkable," Vanier said after his speech on Sunday. "They have immense numbers of friends in the street . . . so it's not just a house, it's a house integrated into the neighborhood." .

Though L'Arche and COTA are not affiliated with any church, they consider themselves a spiritual organization. Vanier's speech borrowed much from his own Catholic faith.

Bruner, who has worked with handicapped people since she was a teen-ager in Washington, said she was particularly drawn to L'Arche because of "the faith element, which is very important to me.

"The people in the house all belong to different churches. But all people have the right to some sort of spirituality, and not to have that denied them because they are mentally retarded. It's important that it be a choice," she said.

Bruner said COTA plans to open another L'Arche-affiliated house in Adams-Morgan next year, with the help of a $20,000 donation from an elderly Florida couple who have two mentally retarded children in the Washington area.

According to COTA, 3 percent of the national population is mentally handicapped, and that houses such as the Adams-Morgan facility give them one alternative in group living. "You don't have to be a psychologist to live in a house with someone who's mentally retarded," said Bruner.

Vanier recounted to the audience at the Shrine how L'Arche celebrated its 20th anniversary at its home in France.

"We rented a boat on the Seine, and all 400 of us went for a ride . . . . It typifies what we've discovered about celebration . . . being together, giving thanks because we are bonded together and we know that we'll never be lonely again."