Community groups opposing Bruce Ratner’s Atlantic Yards development in Brooklyn are advancing an alternative proposal to develop the site. The “unity plan” calls for the development of the 11-acre rail yard but does not include a new home for the New Jersey Nets.

Mr. Ratner’s plan covers a 21-acre site – comprised of the rail yard and surrounding streets – that he hopes to develop through a combination of private purchases and eminent domain. The developer bought the Nets last year and hopes to move the basketball team to a 19,000-seat Frank Gehry-designed arena to be built at the site.

The community groups Develop Don’t Destroy Brooklyn and Park Slope Neighbors are scheduled to present their plan this evening at a community meeting in Park Slope.

“The point of the unity plan is to elevate the discussion away from the arena and try to make it about real issues, such as the value of the Atlantic Yards to the community,” the director of the Atlantic Yards Development Workshop, Marshall Brown, said. The workshop is the architecture group that designed the unity plan.

“It is about stitching communities together by creating new street connections and public parks so the rail yards fill in the gap between Prospect Heights, Fort Greene, and Park Slope rather than act as a wall, as in the Forest City Ratner plan,” Mr. Brown said.

The spokesman for Develop Don’t Destroy, Daniel Goldstein, said: “The idea isn’t to make a huge profit with public money, but to make sure the profit goes toward the community’s needs instead of a private developer’s bottom line.”

A spokesman for Forest City Ratner said the company was familiar with the plan but believed it was not a realistic alternative.

“We’re taking a look at the plan, but based on what we’ve seen it is not feasible,” the spokesman, Joe DePlasco, said. “They have no way to pay for it, while under our plan we have private funding in place and the expectation of city and state funding that will be more detailed when we issue a memorandum of understanding.”

The unity plan at the Atlantic Avenue Rail Yards, which is at the intersection of Atlantic and Flatbush avenues two blocks from the Brooklyn Academy of Music, would have 60% to 70% of the density in terms of square footage of the Ratner plan, according to Mr. Brown. While the Ratner plan calls for 300,000 square feet of retail space and several high-rise towers, the unity plan makes room for 700,000 square feet of retail space and an average building height of 10 stories.

Mr. Brown said the unity plan emphasizes affordable housing, but it makes no mention of the number of housing units that would be created by the development. The Ratner plan, which extends beyond the rail yards to include the arena and 2.1 million square feet of commercial space, makes room for 4,500 housing units.

“Our plan does a number of things the opposite of Forest City Ratner. For example, while their plan calls for the de-mapping of streets, such as two blocks of Pacific Street, we extend streets to connect neighborhoods together,” Mr. Brown said. Streets that would be extended under the unity plan to create more lot frontage and pedestrian walkways include South Oxford, Cumberland, Adelphi, and Clermont Avenue.

“Rather than one monolithic site, we are also dividing the yards into multiple plots so smaller developers and community groups could develop it in a more organic way over time,” he said.

Indeed, a developer who owns 120,000 square feet of property in the Ratner footprint, Henry Weinstein, said: “The air rights over the rail yard haven’t been offered to anyone but Ratner, but if there was a competitive bidding process, there would absolutely be a number of developers – including myself – interested in the site.”

“The unity plan,” Mr. Weinstein said, “is a good alternative and is definitely feasible.”

The City Council member who represents the Atlantic Yards neighborhood, Letitia James, said: “The community is not antidevelopment, it just opposes eminent domain.”

Ms. James, who was a sponsor of the unity plan, said: “Ratner only owns about one-third of the private property he needs for his plan, according to the residents and business owners who live inside the footprint who I have spoken to.”

Said Mr. Marshall: “The unity plan is not about demonizing Forest City Ratner, or even about criticizing the plan, but about criticizing the process – or the lack thereof. The mayor, the governor, and the Brooklyn borough president see it proper to give a piece of land at a sweetheart price to a developer who threatens the condemnation of homes.” He said the City Council or local community boards should have responsibility for oversight of the plan.