Fourth Avenue is on the verge of becoming one of the densest new residential areas in Brooklyn, experts say, with close to 1,000 apartments under construction on a 1.4-mile stretch of six-lane road known for its car repair shops, gas stations, and big box stores.

Half of the first buyers in the 20 new buildings come from just up the way in Park Slope, according to sales directors.

“When I first moved in Park Slope in 1996, I wouldn’t even consider living on Fifth Avenue, much less Fourth Avenue, but things are changing,” Renato Poliafito, who recently bought a one-bedroom at the Argyle, a 59-unit project on Fourth Avenue and 7th Street, said.

“I missed out on a two-floor apartment in Park Slope for $110,000 in the 1990s,” Mr. Poliafito, who runs a bakery in Red Hook, said. “I’m tired of missing opportunities.”

Mr. Poliafito, 34, and his boyfriend acquired the sixth-floor one-bedroom for slightly more than $500,000.

The Argyle, which is now about 60% sold after six months on the market, is one of three buildings on the street that have begun selling units. The others are the Novo at Fourth Avenue and 4th Street and the Crest at Fourth Avenue and 2nd Street.

“If you love Park Slope and you live here now and rent, but have a home that is too small for your growing family, this is a great benefit,” a senior sales director at Massey Knakal, Kenneth Freeman, said.

Still, the Novo, the largest development, is struggling, with 57 of 151 apartments, or 40%, sold after more than a year on the market and a round of price cuts. The Crest, on the other hand, has done well, selling 57 of 68 units, or 80%, after eight months on the market. It will be the first building ready for occupancy, with new residents planning to move in this weekend.

All three buildings have listings for between $700 and $800 a square foot, which is about the same as Park Slope and other higher-end neighborhoods in Brooklyn, according to 2007 sales reports.

“This neighborhood is starved for new condos and developments,” the sales director of the Crest and the Novo, Steven Laurelli, said.

The other major developments planned for Fourth Avenue include a 12-story, 137-unit building at 12th Street and a 12-story, 94-unit building at Butler Street. A planned upzoning of major thoroughfares in nearby Sunset Park could render Fourth Avenue one of the densest new residential areas in Brooklyn, experts say. The softening real estate market, however, is expected to temper this growth somewhat.

“The pace has slowed because of the market, but you can’t walk a block without running into a new building,” the chairman of Community Board 7, Randolph Peers, said. “There is a possibility of this reaching even farther up Fourth Avenue.”

Some members of the community have voiced concerns about the new developments, noting that not one of the buildings has taken advantage of a deal that allows developers to build taller buildings in exchange for including affordable apartments. And little or no space has been devoted to street-level retail, critics say.

“The grand plan of having Fourth Avenue become the ‘Park Avenue of Brooklyn’ is coming back to slap city officials in the face,” a founder of Concerned Citizens of Greenwood Heights and a Community Board 7 member, Aaron Brashear, said. “The buildings are ugly and architecturally devoid. They are more of a dormitory style than high-end buildings.”

A widely circulated article on the Web site Streetsblog.org describes the Novo as a “sidewalk disaster” and “looming fortress-like over a playground.”

“Instead of transforming Fourth Avenue into Brooklyn’s next great neighborhood, these new developments turn their back on the public realm, burdening the street wall with industrial vents, garage doors, and curb cuts,” the article, headlined “New York Can Do Better than the ‘New Fourth Avenue,'” said.

For now, the new residents will live in the Manhattan-style condos on Fourth Avenue while shopping and socializing blocks away, near the more retail-oriented Fifth and Seventh avenues.

“In a few years, Fourth Avenue will probably change, but the rest of Park Slope and Red Hook is just a bus ride away, or I can take my bike,” Mr. Poliafito said. “Most of the buildings right now look sterile, but they are definitely more affordable than a brownstone.”