The group's plan is to transform the five-building campus – a church, convent, rectory, and two schools – into a mix of affordable and market-rate housing, schools, retail space, a green corridor, and single-room-occupancy units operated by the Pine Street Inn.

The plan preserves four of the existing buildings and would demolish the rectory.

A neighborhood history and preservation group, Historic Hyde Square, is opposing the demolition plan, which would replace the rectory with a four-story retail and residential building that developers say is essential to making the project work financially.

Rik Ahlberg, founder of Historic Hyde Square, argues that the rectory, like all of the buildings on the Blessed Sacrament site, should be preserved.

''There are many beautiful old buildings in Hyde Square, but these five are most significant," he says. ''It is important to honor them, to be good stewards." The rectory, built in 1894, ''is in good structural condition and doesn't need to be torn down. The original slate roof, front entry, and much of the front porch are still intact."

Richard Thal, executive director of the neighborhood development corporation, said the group has investigated alternatives to demolishing the rectory, including building around it, moving it closer to the street to make it more attractive to potential retail tenants, or relocating it to a different part of the site. Demolition, he says, is the best option.

''For this project to meet the needs of the community and be economically viable, it needs to include approximately 11,000 square feet of retail, in addition to residential units," he says. ''The rectory doesn't provide that kind of workable retail space."

Ahlberg, a director of technology at an investment firm, argues that with four entrances, the rectory easily could be subdivided for retail or other uses, and says its historical character would make it attractive to potential tenants.

''The iron fence and granite walls around the rectory are beautiful details that should be enhanced, not eliminated."

Ahlberg launched Historic Hyde Square with a website in 1999, and says his organization is primarily an ''information clearinghouse for neighborhood history" rather than a membership organization. His efforts, he says, are about respecting history.

''Buildings tell a story, and they need to be preserved to keep the story intact."

Thal contends that the Jamaica Plain Neighborhood Development Corporation has worked to balance preservation concerns with the need for more affordable housing. Current plans call for 52 mixed-income condos, 36 affordable housing co-ops, and 27 single-room-occupancy units.

Thal says his group will make a presentaion in late March to the Boston Landmarks Commission, the agency responsible for identifying and preserving historic properties, and then submit its site plan to the city for review.

Seth Gitell, a spokesman for the mayor's office, said the commission won't comment on Blessed Sacrament until it has received a formal application.

Ahlberg says that Historic Hyde Square will be advocating for preservation during every step of the review.

''Once any of these buildings are gone, they're gone forever," he says. ''There's only one chance for a preservation-oriented redevelopment."