Livid with a former neighbor they said sold them out, angry with a process they said shut them out, and concerned over a facility whose inhabitants' identities will be guarded, Cedar Grove residents loudly voiced their opposition Tuesday to a planned home for mentally challenged adults.

The plan of Bay Cove Services to locate a six-person residential facility at 53-55 Chelmsford met with stiff resistance in a crowded Cedar Grove Civic Association meeting in the basement of St. Brendan's Church, prompting Bay Cove officials to acknowledge they might reconsider.

"We're certainly going to go back and think about the concerns of the community," said Bill Sprague, executive director of Bay Cove, a Boston-based, private non-profit that administers to more than 6,000 mentally ill, disabled, and addicted annually.

The two-family on Chelmsford Street, quietly sold last month for $640,000 by the Keating family, would offer confidential residence to mentally challenged adults.

Cedar Grove residents ripped the purchase-and-sale proceedings, which are nearing their final stages.

"The process was flawed from the very beginning," said John O'Toole, president of the civic group. "The vacuum of information from the seller and the buyer to the community is completely inexcusable."

Calling the Keatings' departure - a hushed exercise - "the midnight move," activist Kevin Monahan said his daughter had babysat last month for the family, and they'd made no mention of the deal.

"Bay Cove and the Keatings have insulted the community by their lack of communication and engagement," Monahan said. Taking pains to laud Bay Cove's "noble work," he added, "The failures of the buyer and the seller have poisoned this transaction."

Sprague said Bay Cove policy is not to contact neighbors until after acquiring a property.

"We try to run residential programs in a way that makes us good neighbors," Sprague said. "I'm here to commit to you tonight that we would be a good neighbor. We've done this before. It's very hard for me to convince people of that in advance."

City Councillor Maureen Feeney said she felt betrayed by Bay Cove, on whose board of directors she sits. Feeney called the period since she learned of the sale "probably … the most difficult two weeks or nine days … of my entire political life."

Fighting back tears, Feeney said Bay Cove should have conducted a more thorough community process, and she called Kevin Keating, the property's former owner, "a greedy son of a [expletive]."

Several people said local residents have offered to buy the property, which city records show to be valued at $406,000.

Patrick Connolly, who lives at 65 Chelmsford, named several Bay Cove facilities in Dorchester, home to roughly half its Boston service centers.

"I think these residents do their share," he said.

State Senator Jack Hart said neighbors were worried that Dorchester was turning into a "social service mecca."

It was the second case within a week in which Dorchester neighbors found themselves in the uncomfortable position of opposing disability advocates. In Savin Hill, residents are battling for an earlier reopening of the T station there, while a state board says the station cannot open until it is in compliance with federal disability guidelines.