The owners of the 45-acre NorthPoint development site in East Cambridge have offered to support a proposed bailout of the MBTA’s troubled Green Line Extension project.

Cambridge and Somerville officials said Thursday they will seek local and state approval to contribute $75 million toward the 4.7-mile trolley line from Cambridge’s Lechmere station to College Avenue in Medford near Tufts University.

State transportation officials are set to discuss the latest funding proposition for the project Monday, after divulging last year that estimated costs had ballooned from $2 billion to $3 billion.

Since then, consultants have studied cost-cutting redesigns, including a reconfiguration of a $100 million walking path to save $80 million, elimination of public art projects and scaling back of station designs.

San Francisco-based DivcoWest acquired the largely undeveloped NorthPoint site for $291 million in a partnership with HYM Investment Group of Boston last year. The site has been permitted for 4.5 million square feet of development since 2003, but delayed by lawsuits and market fluctuations.

The developers’ as-yet unspecified financial contribution would be part of Cambridge’s $25 million share of the bailout. The private contribution toward Green Line Extension infrastructure runs in the “tens of millions” of dollars, according to a joint statement released by the two cities. As part of the extension plans, the aging Lechmere station would be relocated next to the NorthPoint property on the east side of Monsignor O’Brien Highway.

The local contributions are subject to approval of the Cambridge city council and the Somerville board of aldermen.

DivcoWest and HYM are expected to begin permitting for the first phase of commercial development at NorthPoint as soon as next month, hoping to cash in on intense demand for office and lab space in the tight East Cambridge market. Cambridge officials last July also approved up to 50,000 square feet of retail space at NorthPoint including a supermarket.

A spur of the Green Line Extension is also a lynchpin of a $1 billion redevelopment effort in Somerville’s Union Square. Chicago-based master developer US2 plans up to 2.3 million square feet of commercial and residential development on 15 acres near a new Green Line station.

Amid increasing fiscal demands from the MBTA’s aging equipment fleet, state transportation officials have started to partner with private developers on design of transit stations near new projects. NB Development is paying for the estimated $16 million commuter rail station under construction on the MBTA’s Framingham-Worcester line next to its $500 million Boston Landing complex in Brighton.

The MBTA Fiscal and Management Control Board and the MassDOT board of directors will meet Monday to review a revised budget and decide the future of the Green Line Extension project.

Also as part of the bailout, the Boston Region Metropolitan Planning Organization will move about $190 million toward the construction of the seven new Green Line stations in Cambridge, Somerville and Medford, MBTA Advisory Board Executive Director Paul Regan told the State House News Service. That money was originally set aside for an eighth station at Route 16 in Medford.

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 a new transit stop.

Draisen noted Medford lost funding for the eighth stop at 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,” Draisen said.

Somerville Mayor Joseph Curtatone and Cambridge City Manager Richard 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.

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.”

Information from the State House News Service was included in this report.