The city is examining a request to create a new historic district in NoHo, potentially adding to the growing checkerboard of Lower Manhattan neighborhoods where development is constrained under preservation regulations. Downtown preservation advocates are also pushing for the designation of a sweeping 400-building area on the Lower East Side and another in the southern part of Greenwich Village.

When designated, neighborhoods receive a new layer of regulations on all buildings and lots in the district to ensure that any construction fits within the character of the district. Landlords and developers are often aggravated by these restrictions while preservation advocates hold them up as playing a crucial role in maintaining neighborhood character.

A spokeswoman for the city’s Landmarks Preservation Commission, Elisabeth de Bourbon, said the agency is evaluating 50 buildings on multiple blocks in NoHo, just east of NYU’s Washington Square campus, and no timeline has been set.

The chair of the NoHo Neighborhood Alliance, Zella Jones, said she has been pushing for years for the city to give landmark designation to the whole neighborhood, which contains numerous buildings constructed in the 19th century. While the city designated one piece of the neighborhood in 1999 and another in 2003, it has not moved forward on a third section which stretches along Bond and Great Jones Streets, between Bowery and Lafayette Street, until now.

With the area unprotected, developers have built on numerous vacant lots in the past few years, Ms. Jones said, some of which she finds out of context.

“It really changes the look of the street a great deal and changes the way that you look at buildings,” she said.

In recent years, the area of Manhattan south of 14th Street has seen a boom in new residential building, and an outcry from residents who wish to bring new development in line with the area’s existing low-rise composition. Preservationists have scored some victories, as in the designation of the Meatpacking District, and some defeats, like the 45-story Trump SoHo expected to rise near the Holland Tunnel.

An attorney at Hartman and Craven who works with zoning laws, Juan Reyes, said that new preservation rules can irk developers that were previously expecting a quicker building process.

“It does have an effect on all development in the area because there’s another layer of approval,” Mr. Reyes said.

The director of the Greenwich Village Society for Historic Preservation, Andrew Berman, said the land where many of the designations are occurring are vibrant as a result of their historic character, not in spite of it.

“We’re talking about some of the most prosperous neighborhoods in all of New York,” Mr. Berman said.