Twenty-nine percent of public school families on the Upper West Side would be zoned to new elementary schools under a plan being floated by the Department of Education that is sure to unsettle parents and possibly even the real estate market.

Another proposal would rezone fewer families by moving two coveted West Side institutions, the Anderson School and the Center School, into new buildings.

The rezoning is being considered as an attempt to relieve overcrowding by shifting some of the students in areas with too many to zones that have more room to grow. For example, under the first proposal, families who live in some parts of the West 60s would be pushed to P.S. 87 from P.S. 199, and families who live in some parts of the 80s would go to P.S. 9 from P.S. 166.

The rezoning cannot happen without the approval of the district’s elected parent group, the community education council, and it would not affect students who are already enrolled at schools.

The abundance of possible changes is already rattling parents. Some worry that younger siblings will not get to go to school with their brothers and sisters. Others at Anderson and the Center School are afraid that moving their schools to new proposed sites would hurt their children’s experience.

“Whenever you change zoning lines, somebody’s going to be going to a school they wanted to go to, and somebody is going to be zoned out,” a member of the community education council, Jennifer Freeman, said.

A school official who is coordinating the rezoning, John White, said the proposals are meant not as final answers, but to start a conversation about the best solution to the overcrowding problem.

“What we’re trying to do is ask the CEC to engage us and engage the community as to which trade-offs should be made,” Mr. White said in an interview yesterday. “We need to make the best trade-offs working with the community.”

When rezoning was first raised as a possibility, a major concern stated by parents was that those who had moved to certain neighborhoods for the sake of their zoned schools would be reassigned to less-desirable ones.

Neither proposal appears to force such a situation; families zoned for the two most highly coveted elementary schools, P.S. 187 and P.S. 99, would only switch between the two if they switched at all, and no one from either school would be rezoned to the elementary school to the south, P.S. 191, which is less popular.

Still, a range of other possible changes are raising concerns.

Ms. Freeman said the community education council is waiting to collect more people’s opinions before putting out a formal response. The council has scheduled a meeting tonight to do so.

Ms. Freeman she said she has found dozens of small problems. One is that the proposals do not include any plans to construct new buildings.

“Building new capacity has to be part of the solution or you don’t really get to a solution,” Ms. Freeman said.

Mr. White said that if there is new construction, it would be charted out in a separate process, through the capital plan.

Another point of concern is the so-called choice programs that allow families across the school district to attend schools outside their official zone. The district, District 3, includes not just the Upper West Side proper, below Morningside Park, but also areas north of the park in Harlem.

Many families use district-wide kindergarten lotteries and gifted and talented programs to pull their children away from their neighborhood zoned school and into more coveted programs and schools.

If new zoning lines send more neighborhood students to schools where such programs are popular, those programs could be put in jeopardy.

In an interview, Mr. White said that gifted and talented programs would not be eliminated but might be moved to a school with more open space.

He said lotteries that pull students into kindergartens outside their neighborhood schools could also be questioned.

“We’ll have to work with the CEC on this, but we might be led to conclude that in some places, if we want to rezone, the implementation of the lottery is no longer the best thing for the schools,” Mr. White said. “And in some cases we might decide that it is.”

Eliminating or moving some choice programs would free up space at several schools. For instance, P.S. 87 on 78th Street would be at 50% capacity if only neighborhood students zoned for the school attended.

Moving the programs would also upset many parents who send their children there from outside the neighborhood, many of them through kindergarten lotteries.

“If they did away with the lottery, then all these overcrowded desirable schools would no longer be overcrowded,” a commenter on the Web site Urban Baby said. “I say, if you buy a townhouse in Harlem, be prepared to send your kids to school there.”