The president of the Bronx, Adolfo Carrion, will lend his support to the new Yankee Stadium project at a city planning commission hearing today.

If approved by planning and the City Council, the new 51,800-seat stadium will cover about 22 acres and wipe out roughly half of Macomb’s Dam and John Mullaly parks. The state Legislature and the council have already approved the transfer of parkland to the Yankees.

Mr. Carrion today will insist that the parkland be replaced before construction begins. The borough president, who is seen as a potential Democratic mayoral candidate for 2009, recently approved the Yankees’ land use application with a list of nonbinding conditions.

That might not be enough to satisfy a contingent of neighbors who say the project will eradicate the South Bronx’s “Central Park” and replace it with inferior and hard to reach park facilities.

Community organizers say about 150 opponents of the project will be in Lower Manhattan today to testify before the commission. Their other complaints include increased traffic, the amount of public subsidies, the lack of a community benefits agreement featuring promises of permanent jobs, and the potential negative public health effects of the construction. Opposition groups have met several times in the last week to coordinate testimony.

Gregory Bell, the chairman of a neighborhood organization that opposes the plan, the Bronx Voices for Equal Inclusion, said yesterday, “We have done our homework.”

He added: “We would desire to have economic development in Bronx County, but not at the expense of the park. We are trying to shape the project in such a way that it is beneficial to the community.”

Through a spokeswoman, Alice McGillion, the Yankees said they have made changes to their land use application to mitigate some of the neighbors’ concerns. Three ballfields that were originally slated for a riverfront location, which would have required residents to cross the Major Deegan Expressway, have been moved closer to the neighborhood. In addition, a parking lot that would have cast a shadow over some parts of the area has been lowered.

A member of the City Council, Helen Foster, the lone elected official who has been outspoken against the project, charged that the Yankees’ disregard for the local community is an old pattern.

“The organization itself has not been a good neighbor for years. Going forward, we can’t rely on good faith or trust, because I don’t think any of that is there,” Ms. Foster said.

The Yankees will pay about $800 million for the new stadium. The city and state will contribute about $300 million for the new parking facilities, parks, and infrastructure improvements.

The stadium is not the only project in the pipeline for the South Bronx, long one of the city’s poorest neighborhoods. The council will soon consider an application by Related Companies for a $394 million mega-mall just south of the stadium on the site of the Bronx Terminal Market.

In addition, Boricua College has applied to open up a campus and dormitories near the Bronx criminal courthouse. There are also plans for several new residential developments along Grand Concourse Avenue.