Transit official Katherine Fichter speaks at a Kendall Square green line extension meeting May 26, 2010, when construction was scheduled to be done in 2015. (Photo: Marc Levy)

Mass transit officials working on the green line extension have scheduled a meeting for Sept. 13 in Boston to talk about the three- to five-year subway construction delay. Public comment will help direct a group being formed to improve the schedule, the officials said in a Monday press release.

Once expected to be done in early 2015 with rail all the way to Route 128 through Somerville and Medford, the latest delay has the project done as late as 2020 but only as early as 2018.

People are “angry and frustrated,” it’s been noted over at The Somerville Transporation Equity Partnership, whose site hosts a petition to get the work back on track.

Transportation officials at the Massachusetts Department of Transportation and Massachusetts Bay Transit Authority acknowledge the emotion.

“We understand these concerns and want to emphasize that MassDOT and the MBTA are in no way choosing to delay the Green Line Extension project at this point,” said Katherine Fichter and other officials in the e-mailed press release. “The new schedule reflects what we believe to be a realistic and reasonable assessment of how long the project will take to complete from its current point of development, given the many complex, interrelated and time-consuming tasks remaining.”

“We are not slowing the pace of our work or reducing our commitment to seeing the project through,” they said. “MassDOT and the MBTA are not satisfied with the current anticipated schedule for the Green Line Extension project.”

The agencies have called for the creation of a small steering group to consider ways to improve the schedule, they said. The Steering Group is begin its work in September.

There will be two meetings to discuss the agencies’ steps. Both are Sept 13 at the Washington Street Conference Center’s second-floor rooms A, B and C at 1 Winter Street in Boston. The meetings are scheduled for 1 and 5 p.m., with the later one to be extended “as needed to allow for all interested parties to present testimony.”

The green line extension project moves the Lechmere stop to the NorthPoint development side of Monsignor O’Brien Highway; adds a one-stop spur to Union Square in Somerville, roughly where Prospect Street and Webster Avenue meet; and lengthens the line through Somerville into Medford, including to Brickbottom, Gilman Square, Lowell Street, Ball Square, College Avenue and finally to Route 16, to a site near the Starbucks, Whole Foods Market and U-Haul depot. Officially, after a first announced delay, all but the outermost stop were to be built by October 2015.