The Green Line Extension moved one step closer Monday toward the goal of federal funding, though there is no guarantee the federal government will eventually cough up money to help pay for the project.

According to a letter sent Monday by the Federal Transit Administration to Richard Davey, secretary of the Massachusetts Department of Transportation, the Green Line Extension has been added to the pipeline of projects in the federal administration's New Starts program.

The letter says the Green Line Extension has permission from the administration to enter the "preliminary engineering" phase of planning.

This puts the proposed Green Line Extension on a master list of transportation projects across the country the Federal Transit Administration is considering for federal funding.

It is not a guarantee the project will get federal assistance, but it's a necessary step for all projects seeking New Starts funding. It's also an initial stamp of approval from the feds.

Projects begin their life on the New Starts list in the "preliminary engineering" phase. They then move to the "final design" phase, and ultimately, if the Federal Transit Administration decides to award money to the project, to the "full funding grant agreement" phase. The Green Line Extension, which would extend the MBTA's light rail subway line into Somerville and Medford, has a long way to go before it reaches that point. 

According to the letter, the estimated cost of the Green Line Extension is $1.3 billion, and Massachusetts is asking New Starts to pay for $557 million of that, about 41.7 percent of the total cost.

The letter, while accepting the Green Line Extension into the New Starts pipeline, does express concern about the project and the MBTA's financial situation.

The state's financial plan for the MBTA includes transferring $1.6 billion of MBTA debt to the state, implementing a $0.01 per mile statewide tax on vehicle miles and allocating casino gaming revenues to the MBTA, measures the letter calls "large new, uncommitted fudning sources."