Officials from Somerville and Cambridge said Thursday they expect to contribute a total of $75 million, part of an "unprecedented arrangement," to help complete a scaled-down Green Line Extension project.

Somerville is expected to contribute $50 million in "new financial participation," and Cambridge, along with developers of North Point near the Lechmere Station in that city, is projected to make a contribution valued at $25 million, according to an announcement by the two cities.

The trolley extension project is in limbo after state transportation officials warned last year that its projected cost had increased from about $2 billion to as much as $3 billion, forcing state officials to reexamine the project's scope as well as its spending and revenues.

The $75 million in new revenue is needed to "close the funding gap," and would be subject to local approval, according to the statement from Somerville Mayor Joe Curtatone and Cambridge City Manager Richard Rossi. Rossi visited the state Transportation Building on Monday where he said he was seeking more information about the city's contribution.

"Expanding this financial partnership is an extreme and unprecedented arrangement for a state infrastructure project," the announcement stated. "Despite the fact that our cities bear no responsibility for the cost overruns that brought the GLX to this moment of crisis, we will seek to support the Commonwealth by expanding our cost-sharing role. The Green Line is that important to our communities, our region, and our state."

The MBTA has been working on new project scope and cost estimate and says it will be discussed at a joint meeting of MBTA and state transportation boards on Monday, other financial moves have occurred.

As state and MBTA officials are set to discuss the future of the trolley extension, deliberations over the local contributions will shift to the Cambridge City Council and Somerville Board of Aldermen.

MBTA Advisory Board Executive Director Paul Regan told the News Service that state transportation officials on Thursday requested the Boston Region Metropolitan Planning Organization move about $190 million into the construction of seven new Green Line stations in Cambridge, Somerville and Medford.

Regan said the proposal would move the funding out of a proposed eighth station at the end of the Green Line Extension, near the Medford-Arlington border.

Regan said the move would not violate the vote transportation officials made in December to restrict additional state funding to that "set forth by federal requirements only."

Locally governed, the organization receives 80 percent of its funds from the federal government and 20 percent from the state, Regan said. Regan said state transportation officials would not disclose the new bottom-line of the project to the planning organization.

Metropolitan Area Planning Council Executive Director Marc Draisen said the $75 million pledged from Cambridge and Somerville represents the total local contribution even though Medford would also receive new transit stops.

Draisen noted Medford lost funding for the eighth stop along Route 16 and said the city has limited ability for commercial redevelopment on its portions of the remaining project.

"We thought it was fair distribution," said Draisen. An unspecified portion of the Cambridge contribution would come from developers of North Point, in the area of East Cambridge where a rebuilt Lechmere Station would go.

Curtatone and Rossi said they understood that without "firm financial commitments," the area would lose out on the project, estimated to have already incurred about $700 million in sunk costs and due to potentially receive a nearly $1 billion federal grant.

The project will retain elements deemed at risk of being cut, including a trolley station in Somerville's Union Square neighborhood and a community path, according to Curtatone and Rossi.

Rafael Mares, vice president at the Conservation Law Foundation, said the organization is pleased the city leaders recommended "significant contributions."

"This transit project is of great importance not only to both of these municipalities, but also the region and the state," Mares wrote to the News Service in an email. "As such, we expect that the MBTA and MassDOT will decide soon to move forward with the project."