PORTLAND — The Planning Board tonight will vote on a controversial plan to establish offices in the parish house of the Williston-West Church.

The epic zoning battle, which involves one of the city’s most important buildings and some of the city’s most prominent residents, will then move to the City Council, which will make the final decision when it takes up the issue, likely in June.

Rezoning the Thomas Street parcel to allow for commercial office space could have an impact elsewhere in the city by setting a precedent for how the city’s comprehensive plan is interpreted, said City Councilor David Marshall, who represents the West End and has yet to decide how he will vote on the plan.

“It’s an incredibly complex political issue,” he said.

Built in 1877, the Williston-West sanctuary was designed by Francis Fassett, a prominent architect. In 1904, John Calvin Stevens, Portland’s most famous architect, built the parish house next door.

The Planning Board is recommending that the current residential zone be changed to allow offices for up to 14 workers in the church’s parish house.

Australian businessman Frank Monsour, who bought the church in December, plans to use the first floor of the parish house as the U.S. headquarters for his software development company, Majella Global Technologies.

He also plans to establish two or three residential units in the upper floors and preserve the sanctuary as it is so it can be a community hall.

The rezoning agreement would require that he restore the parish house and sanctuary. Monsour said he would spend up to $1 million renovating the building, including replacing the leaking asphalt roof with a slate roof.

The proposal has drawn the attention of West End residents and preservationists. The Planning Board has received 91 written comments, 32 in support and 36 opposed. It has also received a petition in opposition signed by 140 people, three of whom later contacted the city and lasked that the names be removed.

The proposal will enhance the city’s architectural heritage and strengthen the city’s economy, Hilary Bassett, executive director of Greater Portland Landmarks, told the Planning Board tonight.

“The preservation of the Williston-West complex is important, not only for the neighborhood but the entire city,” she said.

At stake is the future of the church complex, which is on the National Register of Historic Places but now has serious deferred-maintenance issues, said Paul Stevens, a prominent architect and the grandson of John Calvin Stevens.

“Our opponents tonight would sacrifice a very important building for the purity of (residential zoning) language,” he said.

But zoning rules that protect residential neighborhoods should not be overridden, especially for a business that does not serve the neighborhood, said Anne Pringle, a former Portland mayor who now heads the Western Promenade Neighborhood Association.

“Historic preservation should not trump residential zoning integrity,” she said.

Pringle and several other residents said that the church complex could be developed for residential use and generate enough income to restore the structures.

The current zoning allows up to four residential units in the complex.

Jonathan Culley, a developer who has converted several West End buildings into residential condominiums, says in a letter to the Planning Board that that site lacks adequate parking and that it would be too costly to convert the church complex to condominiums.

Even if a developer got a zoning change to allow for 10 condominium units, he writes, the project would never pay for the needed repairs and maintenance costs

“The numbers don’t add up,” he says in the letter.