Mayor Bill de Blasio ventured Tuesday night into south Brooklyn, a more conservative corner of the city, for a town hall dominated by quality-of-life concerns.

Residents of Bay Ridge gathered at Fort Hamilton High School to challenge the mayor on the illegal conversion of homes in the area as well as the proliferation of hookah lounges and heroin and prescription drug abuse.

“You’re the guy that can push the department and the agencies to solve this problem,” Bob Cassara, a lifelong Bay Ridge resident, told de Blasio of lack of enforcement of illegal conversions. “As soon as a house is shut down — with a stop-work order — it doesn’t take a week before it opens again.”

The mayor, a Democrat, told Cassara — a Republican and founder of the Brooklyn Housing Preservation Alliance — the last city budget funded 100 new inspectors for the Department of Buildings.

“We’re putting a lot more firepower into the hands of Commissioner [Rick] Chandler and his team,” de Blasio said. “We take it very, very seriously.”

The town hall, attended by about 300 community members and activists, was co-hosted by a bipartisan slate of elected officials representing the Bay Ridge area: City Councilman Vincent Gentile and state Assemb. Pamela Harris, both Democrats, and Republicans, Rep. Dan Donovan and state Sen. Marty Golden.

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De Blasio didn’t hold his first town hall until 21 months into his term. The south Brooklyn event — his fourth question-and-answer forum — followed others in more liberal neighborhoods like Washington Heights, where affordable housing was a chief concern.

Tuesday night’s meeting was also of note because it was held in the the city’s only congressional district represented by a Republican — Donovan.

The mayor, acknowledging the heroin and prescription drug problem in the area, earned nods of approval when he held up a list of 14 pharmacies that would be selling Naxolone, an over-the counter drug that can reverse the effects of an overdose.

He also appeared to please the crowd by announcing the city would not open a prekindergarten center at an 86th Street site community members had deemed too dangerous because of its proximity to the Gowanus Expressway.

Doris Cruz, 69, a Democrat and Bay Ridge resident, told the mayor about long-standing complaints regarding alleged prostitution and drug dealing at the nearby Prince Hotel. The mayor gave Cruz his “personal guarantee” of a crackdown.

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“When you are told there should have been action,” de Blasio said. “There should have been action.”

Asked if she felt reassured by his response, Cruz said: “I will wait and see.” She added that residents were pleased he made the trek to their neighborhood.

Cassara gave a similar response on whether the mayor would increase enforcement of illegal conversions: “We’ll see.”

Gentile noted in his opening remarks that Bay Ridge and surrounding areas are a contrast to the bustle of Manhattan.

“We in this neck of the woods — in south Brooklyn — consider ourselves a small town in a big city,” he said.