At the tail end of 2005, the City Council rejected two Landmarks Preservation Commission landmark proposals, the Austin Nichols building in Brooklyn and the Jamaica Savings Bank in Queens, raising the prospect that the council was becoming a more independent arbiter of which parts of New York are worth preserving.

The council is likely to have another test soon, as the Landmarks Commission’s plan to designate a wealthy enclave of 257 homes in the Riverdale section of the Bronx as a historic district moves forward.

Yesterday, dozens of Fieldston residents weighed in on the proposal at a Planning Commission hearing near City Hall. The Planning Commission is considering whether the proposed designation melds with the area’s existing zoning regulations and the city’s development plans. It will probably vote at its next meeting, on March 8.

Both opponents and advocates expect the commission to approve the application and want to influence the report that it will pass on to the City Council, which has the final review.

The Landmarks Commission is seeking to impose certain restrictions on development that would preserve Fieldston because it is “a rare, largely intact example of a romantic planned suburban community,” according to an official designation report published last month.

A group formed to oppose the designation, the Fieldston Homeowners Association, contends that the area’s character and history can be preserved without additional government regulation. Several residents said yesterday that a historic designation would make it more inconvenient and expensive for homeowners to make changes, additions, or build anew, and said that the designation would potentially lower property values.

Many opponents said they prefer self-governance through an architectural review committee. They pointed to Forest Hills Gardens in Queens as an example of a successful self-governed private community.

One Fieldston owner, Daniel Hort, said the designation would put him at a competitive disadvantage against other properties if he wants to sell.

“What’s the benefit to the residents of Fieldston? The government entering to attack or ultimately cheapen my biggest investment?” Mr. Hort asked.

Advocates of the landmarking, who outnumbered opponents at yesterday’s hearing, said existing regulations do not provide enough protection. “The magic of this special enclave is on the wane” and the community will “embrace the protection and advice that Landmarks offers,” a Fieldston resident, David Sherman, said.

“When will a community such as this ever be duplicated? I’m afraid never,” Mr. Sherman said.

A nearby private school, Horace Mann, previously opposed the designation, but yesterday school officials said they had reversed their opinion and gave their support to the plan.

Opponents and supporters each contended that they outnumber their adversaries. When the Landmarks Commission designated the area in January, it had received about 90 letters from residents who supported postponing the vote.

Yesterday, the Landmarks commis sioner, Robert Tierney, who appeared at the end of the hearing to voice support for the designation, said he believes a “substantial majority” of the community supports the plan.

The local Bronx Community Board approved the plan last year and the president of the Bronx, Adolfo Carrion, supports it.

Should the Planning Commission approve the designation, as expected, the application will first be considered by the council’s landmarks subcommittee, chaired by Jessica Lappin, a Democrat who represents the Upper East Side.

Ms. Lappin told The New York Sun that members of the council typically “give great deference to the view of the local council member.”

“I will do a tour of the area in mid-March and a number of members will join me to examine the issue more fully,” Ms. Lappin said. “I don’t think anyone has made up their mind definitively yet.”

If the City Council seeks to reject the Fieldston proposal, it will have to do so over the head of an enthusiastic supporter – the local City Council member, Oliver Koppell, a Fieldston resident.

“It almost brings tears to your eyes to feel the beauty of this neighborhood,” Mr. Koppell said, adding that the opposition had fallen prey to fear-mongering and misinformation.

An aide for Mr. Koppell, Jamin Sewell, said yesterday that the council member has discussed the designation with “just about every member of the City Council.”

“I don’t think we are going to have such a problem,” Mr. Sewell said. “The most negative thing we heard was that they wanted more information on it.”