Mayor Bloomberg is rejecting calls from lawmakers to make two Muslim holy days official school holidays, saying students cannot afford more days off.

“The truth of the matter is we need more children in school,” Mr. Bloomberg said yesterday. “More, not less.”

Council Member Robert Jackson of Manhattan, who is Muslim, and 12 co-sponsors introduced a resolution this year calling on the state to require that New York City students be given days off for the Muslim holidays of Eid Ul-Fitr, typically in October, and Eid Ul-Adha, which falls in December this year.

“Parents have had to make a decision on whether or not to send their students to school on the holiest day of the Muslim calendar, celebrating the month of the fast of Ramadan, or to send their kids to take a test,” Mr. Jackson said in an interview. “That type of situation should not be.”

A 2004 Columbia University study estimated that 102,000 Muslim children attended city public schools, making them about 10% of the city’s student population.

State Senator John Sabini, who has sponsored legislation that would require city schools to recognize the two holidays, cited the growing Muslim population as the primary reason for the proposed changes.

“I think that the Muslim population in schools is now large enough that we need to talk about it,” Mr. Sabini, who represents parts of Queens, said in an interview.

Mr. Bloomberg said that adding holidays could be a slippery slope that may lead students to miss too much school.

“When you have a city as diverse as we do, with virtually every religion known to man practiced, if we closed school for every single day there wouldn’t be any school,” he said.

He added that he thought schools could still deal appropriately with students who need to take days off to practice their religion without adding official holidays.