A plan to redevelop a valuable piece of Portland waterfront is focusing attention on the sprawling parcel’s past and, according to preservation advocates, its central role in Maine’s industrial history.

And that has led to potentially competing visions for its future.

Greater Portland Landmarks is requesting that the Portland Historic Preservation Board designate the Portland Co. site – at 58 Fore St. – as a historic district.

Such a designation would subject any development plans to greater scrutiny. It also could force the property’s new owners, CPB2, to alter plans for some of the former manufacturing buildings on the site.

“The Portland Company complex currently lacks any protection of its historic resources, which are at risk as development pressure increases on Portland’s peninsula,” Hilary Bassett, executive director of Portland Landmarks, wrote in a letter to Deb Andrews, manager of the city’s Historic Preservation Program.

Casey Prentice, a partner in CPB2, said Friday that the company knew the organization would likely request landmark status for individual buildings. But Casey was somewhat surprised by the nonprofit’s broader request for a historic district.

“We felt the district nomination was a bit extreme,” said Prentice, noting the designation could change the economics of the project and threaten redevelopment.

Portland Landmarks submitted the request early this month after CPB2 filed an application to rezone the 10-acre property as a first step toward its redevelopment. City staffers have recommended the Preservation Board wait for that rezoning process to play out, which could take several months, before considering the historic district designation.

Located at the base of Munjoy Hill within walking distance of the Old Port, the Portland Co. complex has both enormous development potential and significant historical features. CPB2 has not released specific plans for the site, but Prentice has said the company envisions a combination of residential, commercial and office space while maintaining the marina and historic elements of the property.

The Portland Co. began operating at the Fore Street site in 1847 and ceased operations in 1982. The more than 600 locomotives built by the Portland Co. were used by railroads throughout Maine and eastern Canada, as well as companies such as the Northern Pacific Railroad and the Panama Railroad. Hundreds of ships built in Maine’s many shipyards were outfitted with marine engines built in Portland, including the Civil War gunship Agawam and the 280-foot passenger steamer the Portland.

Navigation buoys and lighthouse components also were built at the site, including the cast-iron structure of Bug Light – the small lighthouse in South Portland.

A third-party study of the Portland Co. site commissioned by the city makes a case for preservation of many of the oldest buildings within “one of the most historically important sites in the city of Portland.”

The study by Sutherland Conservation and Consulting states that the Portland Company complex has national historic significance because it appears to be the country’s first site where all aspects of manufacturing railroad equipment – from the foundry to the machine and car shops – were housed in a single complex. The study said the site appears to be the only manufacturing plant still in existence that built locomotives for the Union during the Civil War.

“As such, the Portland Co. complex contains the oldest surviving railroad shop buildings in the nation still within their historic manufacturing complex context,” the report states.

At the state level, Portland Co. provided the heavy equipment that helped Maine’s marine and forest products industries develop. Locally, it is the only existing manufacturing plant among the 33 that were operating in Portland in 1876.

Architecturally, the Portland Co. buildings that date to the 1840s and 1850s “are the only industrial buildings of that period remaining in the city of Portland today,” the report states.

Prentice said the company hopes to preserve the majority of the historic buildings on site, and even planned to seek historic landmark status for some buildings. But he noted that the Sutherland report did not examine the structural integrity of those buildings, many of which have not been maintained.

Prentice also said that the city’s 2002 Eastern Waterfront Master Plan gives equal weight to encouraging long-term maritime uses in the area, increasing connections between the site and the developed waterfront areas, and encouraging “the adaptive reuse and sensitive rehabilitation of historic structures” on the site.

A district designation “would make that vision more difficult to fulfill.” It also would give the city’s Historic Preservation Board much more control over the company’s plans for the older buildings and any new development on site, potentially affecting the economics of the project, he said.

“That additional layer of review might mean no further development,” Prentice said.

Bassett, the director of Greater Portland Landmarks, said in an interview that her organization does not intend to stop development at the site, but wants to ensure its historic character remains intact.

At least one current tenant of the Portland Co. complex is hoping for a “great compromise.”

Sam Smith is a master blacksmith who uses antique equipment, hand tools and 19th-century techniques to forge everything from ship anchors and tools to jewelry in Building 16 in the location of the Portland Co.’s forge. Smith said he has asked CPB2 to allow him to continue operating his foundry and continue restoring the building to its “original glory.” He’s still awaiting a response.

“This place here is the only part of Portland Company still being used for its purpose,” Smith said.