Portland Mayor Ethan Strimling is expressing concerns about the sale of a small piece of city-owned land seen as pivotal to advancing an ambitious redevelopment plan for 10 acres of former industrial land on the eastern waterfront.

Strimling said a plan to sell the 12,000-square-foot lot to the CPB2 development team for $400,000 is a bad deal for taxpayers.

“At the moment, I don’t think I can support it,” Strimling said in an interview Thursday. “It doesn’t feel like we’re getting good bang for the buck for Portland taxpayers.”

The proposed sale was vetted and recommended unanimously by the City Council’s Economic Development Committee.

Economic Development Director Greg Mitchell said the purchase and sale agreement is in line with the guidance provided by councilors and that the sale is key to advancing the redevelopment of the former Portland Co. site. The deal has been in the works since April, he said.

“Without the sale of this triangular piece of real estate and providing certainty to extend public roads and utilities, the Portland Co. project would not happen,” Mitchell said.

Developer Jim Brady, of CPB2, said the transaction would lead to benefits, not only at the Portland Co. site, but other areas on the Eastern Waterfront, including other land owned by the city. Failure to move forward with the sale “would be a big blow to the redevelopment of the entirety of the Eastern Waterfront, not just the Portland Co. site,” he said.

The property was recently appraised at nearly $900,000, but that assessment assumed that the site was accessible by a public roadway, which is not currently the case. The purchase-and-sale agreement would bind the city toward spending an estimated $1.2 million to extend Thames Street by 230 feet to provide a primary access point to the Portland Co. site. Strimling is concerned that the city is selling the property at a reduced rate, while also agreeing to invest additional money into a road. He said the city will suddenly have to come up with an additional $800,000 to fund the road at a time when there are more pressing needs in the city, such as rebuilding the city’s elementary schools.

“This road specifically goes to one piece of property,” Strimling said. “It’s not like we have already decided to spend the money here.”

Mitchell, however, said the road would also provide additional access to more than 2 acres of city-owned land in the area, including the so-called Amethyst Lot that is being redesigned into a public park, as well other private properties in the area. That could spur additional private investment, he said.

Mitchell noted that establishing a more traditional street grid has been a longstanding goal of the city, dating to the 2004 Eastern Waterfront Master Plan, and that CPB2 would need to use most of the city land to build its own access road into the site.

“We’ve been talking about this for over a decade,” he said, noting that the city’s cost of extending Thames Street would be included in next year’s Capital Improvement Plan. “We have negotiated what we feel is a very fair transaction.”

CPB2’s master development plan for the 10-acre site is currently being reviewed by the Planning Board. To be approved, the developer has to prove that it has adequate access to the site.

The proposal calls for 638 units of rental and resident-owned housing, 132 hotel rooms, nearly 60,000 square feet of retail space and nearly 124,000 square feet of office space. A total of 736 parking spaces are proposed for the site, mostly on the ground floors of the buildings.

The project envisions the rehabilitation of seven historic buildings that would form a retail and office center in the middle of the site, which would be accessed by extending Thames Street. Once inside the site, pedestrians and vehicles would share the road in a Dutch concept called “woonerf,” which features shared spaces, traffic calming and low speeds.

Although some buildings may reach 80-90 feet above the lowest point on the site, no structure would be taller than 35 feet above Fore Street, the development team has said.

The plan calls for more than 223,000 square feet of public open space at ground level, including plazas between buildings, waterfront access through a 50-foot-wide easement and view corridors at Kellogg, Waterville, St. Lawrence and Atlantic streets. There would be an additional 72,000 square feet of vegetated rooftop terraces for private use.