A plan by the Trinity School on the Upper West Side to convert an apartment building it owns into condominiums is running into resistance from the building’s residents, several dozen of whom are staff members of the school.

Residents said they are pursuing legal and political paths to blocking the plan, under which the apartment tower, Trinity House, would be sold to a private developer, Pembroke Companies Inc., for a projected $24 million net profit.

Rents at Trinity House — a 200-unit apartment tower on 91st Street between Columbus and Amsterdam avenues — are currently reduced below market rates through a government program known as Mitchell Lama. In June, the school’s board chairman, Andrew Brownstein, and its head, Henry Moses, wrote a memo outlining a deal under which Pembroke would pull the apartments from the program; make the apartments rent-stabilized, and then convert them to condominiums.

Representatives of Trinity School could not be reached for comment yesterday, though a co-chairman of the building’s tenants’ association, James Paul, said a Trinity representative told tenants protesting outside the school yesterday Trinity does not intend to “condo-ize” the building. A spokesman for Pembroke could not be reached.

Mr. Paul said he opposes the sale because it could drive lower- and even middle-income residents from the building.

The deal would also affect several dozen Trinity employees who live in the building. A letter to faculty members obtained by The New York Sun projects that rents on 39 apartments the Trinity School sublets to faculty and staff would rise by as much as $430 a month.

A teacher at the Packer Collegiate Institute in Brooklyn who first moved to the building while he was teaching at Trinity, Eric Weisberg, said he hopes Trinity will back out of the deal — and instead search for a buyer who would preserve its Mitchell Lama status.

“We tell our students that the bottom line is not the only consideration,” Mr. Weisberg said. “Hopefully, you practice what you preach.”