As the Bloomberg administration pushes to open more charter schools, a public school principal is charging that she will have to close the door on her students if she is required to absorb a charter school in her Lower East Side building.

The popular New Explorations Into Science, Technology and Math school, known as Nest+m, is one of two public schools in Manhattan waging battle against charter schools that are scheduled to take over coveted classrooms in September.

“What are we supposed to do, tell parents that we are declining them after we already accepted them?” the principal, Celenia Chevere, said.

Ms. Chevere said she has already accepted an additional 400 students for next year, but that the Department of Education is telling her that she has room for fewer than 200. She is accusing the city of capping enrollment because of the charter school, but the Department of Education said that the limit has nothing to do with the additional school and that the number is based on its annual audit.

Dozens of angry parents crowded into a meeting at the Department of Education’s headquarters at the Tweed Courthouse yesterday to plead with the schools chancellor, Joel Klein, to move the charter school somewhere else, saying it will harm the educational environment at Nest+m, a school for gifted children.

“It’s a mistake,” the president of the PTA, Emily Armstrong, said. “There are so few spots for gifted and talented children, why would you take them away?”

Mr. Klein said the school was among the most underutilized in the district and that it was his job to look after what’s best for all of the city’s 1.1 million school children. Nest+m houses about 700 students, which the Department of Education estimates is roughly half of its capacity. Ms. Chevere disputes that the school’s capacity is so high.

The Ross Global Academy, a charter school modeled after a school in East Hampton, is tentatively scheduled to move into Nest+m in September with 160 students in kindergarten, first grade, fifth grade, and sixth grade. It will expand each year and eventually include students up to 12th grade.

Located near the Williamsburg Bridge overpass just south of Houston Street, Nest+m is so popular that it attracts families from far outside the district, including some that have opted against sending their children to private school. Mr. Klein said only 30% of the students live in the local District 1.

More than half the students at the school are white, while just 10% of the students in the district fit that profile. Meanwhile, an overwhelming majority of students at city charter schools are black and Hispanic.

Parents are planning to rally against the charter school on the steps of City Hall on Friday afternoon. They also have hired a lawyer and are examining their legal options. On Monday, parents and teachers at P.S. 154 in Harlem also are planning a protest against the charter school, Harlem Success, which is looking to open in the school’s building on West 127th Street.

Officials at both schools complained that the city hadn’t properly informed them about the charter schools moving in. Ms. Chevere said she just recently learned from a parent that the Ross school is scheduled to move in. A teacher at P.S. 154 said the school learned about Harlem Success when a parent showed up with a brochure and said she wanted to enroll her child.

The education department said it has not yet made a final decision on where the new charter schools will be housed. The protests are the latest iteration in a struggle over school space flaring up as the Bloomberg administration opens more small schools and charter schools across the city.

Of the city’s 47 charter schools, 22 share space with one or more schools. Another dozen of the publicly funded but independently run schools are to open next year. As many as 10 of those also will share space with another public school.

In recent years, the Bloomberg administration has opened 149 new small schools, including 141 that share a building with at least one other public school.

“No new small school or charter school causes overcrowding in a building – that’s one of those myths that’s been out there forever and it’s just not accurate,” a spokeswoman for the education department, Kelly Devers, said.

“Even with the charters, they are going to be nowhere near capacity,” she said about Nest+m and P.S. 154. The department also questioned Ms. Chevere’s claims that she planned to accept another 400 students in the fall.

In the past, the school has typically increased enrollment by fewer than 200 students a year.

Uptown at P.S. 154, an art teacher and union representative for the United Federation of Teachers, Dawn Brooks-Decosta, said the school couldn’t spare an entire floor for Harlem Success.

“We don’t have any problem with charter schools, but we don’t want them here because it will tear down everything that we’ve built up,” Ms. Brooks-Decosta said.

The United Federation of Teachers is helping to organize the rally on Monday. The executive director of Harlem Success, Eva Moskowitz, has accused the union of spearheading the attack because of its hostility toward her. Ms. Moskowitz served as the head of the City Council’s Committee on Education until this year. She often went head to head with union officials over the teachers’ contract, which she claimed was getting in the way of educating children. The union said it got involved only because it was contacted by parents.

Ms. Chevere said yesterday that the Ross school, which is partnered with New York University, should move into one of the many NYU-owned buildings in the area.

A spokesman for NYU, John Beckman, said, “It’s a public school, it belongs in a public school building.”