PATERSON, NJ – The city’s largest charter school plans to increase its enrollment next September by almost 50 percent.

The Paterson Charter School For Science & Technology is working on expanding to a third building and accept an additional 500 students, which would boost its enrollment to about 1,5708, according to A. Riza Gurcarli, the lead person on its Board of Trustrees.

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The charter school and its prospective landlord are in the process of getting approvals to convert a warehouse at the corner of East Railway and Gould avenues into a facility for students in grades five through eight, Gurcarli said. Under the plan, the school’s building on Wabash Avenue would handle grades k to four and the old Paterson Catholic building grades nine through 12. At present, the school uses the Wabash site for grades k through six and Paterson Catholic for seven through 12.

Officials at the charter school say the expansion would help serve children on its waiting list, which they said usually has more than 1,000 names on it. Every year, about 300 people apply to send their children to Science and Technology’s kindergarten program, but there are just 80 openings, Gurcarli said.

Those slots are filled through a lottery, he said. “Most of the people leave empty-handed,’’ he said. The expansion would allow the charter school to add about 40 slots to each grade level, he said.

Paterson has been one of the places in New Jersey where the issue of charter schools has generated heated debate over the years.

Some people argue that the money allocated for the charter schools undermines efforts to improve the schools run by the Paterson Public Schools. (The charter schools are funded through the local school district’s budget.) Others insist that the charter schools provide a much-needed alternative for Paterson children a good education instead of going to public schools where students perform far below state averages on standardized tests.

“I see this expansion as somewhat of a discredit to our public school system,’’ said Paterson school board member Errol Kerr. “If they thought we were able to serve their kids at the same level, these parents would keep their kids in the public schools.’’

Kerr said he thought the popularity of the city’s charter schools stemmed more from people’s perceptions than actual differences in the quality of education offered. But he said the school district had to work harder to change those perceptions.

“I’m not going to bash charter schools,’’ said Paterson Board of Education President Christopher Irving. “They have a good track record. Clearly, it’s parents’ prerogative to send their children wherever they want.’’

Peter Tirri, president of the union that represents teachers in Paterson Public Schools, said charter schools have been getting special treatment in New Jersey under Chris Christie’s administration. “They have much more freedom to do whatever they want to do,’’ said Tirri, the Paterson Education Association president. “They get all kinds of money from the state. They take the kids they want to take. They run the programs they want. There’s no way we can compete with the chater schools in that situation.’’

Irene Sterling, president of the Paterson Education Fund, said the Science and Technology school may be producing better high school scores than the average for Paterson Public Schools. But Sterling also said that some of the individual public high schools, like HARP Academy, were doing better than the charter school.

Sterling said the charter school’s expansion may help the public district handle some of its space crunch as its enrollment continues to grow.

Parents of children in the Science & Technology school said they picked the charter because of its smaller class sizes. “The classes are definitely smaller,’’ said Sherie Dye, president of the parent-teachers organization at the charter school. “All the kids get individualized attention and that plays a big part.’’

Carol Burt-Miller, a parent representative on the Science & Technology Board of Trustees, said the annual lottery for the slots in the charter school tends to be a heart-breaking process. “Most of them are not able to get their children in and they become very upset,’’ said Burt-Miller. “It’s important to get your child in a good school.’’