A bill requiring the city to notify residents of the opening of group homes or halfway houses in their neighborhoods could substantially slow down deinstitutionalization, advocates for the mentally retarded told a D.C. City Council committee yesterday at a packed public hearing.

The bill would require the mayor to hold a public hearing 30 days before the opening of any nursing home, public shelter, group home, alcoholism treatment center or halfway house, council member Polly Shackleton (D-Ward 3), explained in an opening statement.

In addition, the city government would be required to notify each property owner living near a proposed facility, said Shackleton, who is chairwoman of the Human Services Committee.

The bill, introduced by council member Nadine P. Winter (D-Ward 6) comes at time when the city is under court order to move at least 100 residents a year out of Forest Haven, the city's home for the mentally retarded, and at a time when residents are fearful of halfway houses, jails and homeless shelters opening in their communities.

"The passage of this bill will profoundly affect the lives of people," said Sharon Raimo, a Ward 6 resident who is the surrogate parent of a former resident of Forest Haven. "People who have waited in most cases too long to take their rightful place in the community in which they were born."

But Winter interrupted the hearing several times to explain that her intent was not to keep mentally retarded persons out of neighborhoods.

"I have a niece who is retarded," said Winter. "This bill is not against any particular group. What I'm objecting to is mixing homes for the retarded with halfway houses and other facilities on the same block."

Winter occasionally referred to city plans to turn the old 9th Police Precinct house at 525 Ninth St. NE into an emergency jail. Winter joined a group of her constituents in successfully delaying the opening.

Winter said she drew up the proposed "public shelter" bill after several members of the Advisory Neighborhood Commission visited her to complain that group homes were opening in their neighborhoods without their knowledge.

Shelore Williams, acting president of the Tubman Neighborhood Association in Northwest, said, "My association's interest in the group homes issue was precipitated by the surprise opening of two new group homes in our neighborhood . . . . " Williams said Ward 1, where she lives, has "62 group homes. Our neighborhood continues to be disproportionately impacted by the placement of additional homes."

But opponents dominated the hearing and many offered eloquent and emotional testimony about the mentally retarded.

"By passing this bill . . . the council will politicize the process of moving into a neighborhood group home," said Harold Evans, father of a severely handicapped daughter, whose class-action suit resulted in the court order to close Forest Haven. "It is clear to me while many people believe in deinstitutionalization , not many people want a home on their block."