Supporters of the Sonoma-Marin Area Rail Transit system are planning a rally at noon Thursday at the Railroad Square site where a transit station is planned.

The rally is in response to the effort by RepealSMART to put a measure on the ballot next year to repeal Measure Q, the quarter-cent sales tax passed by voters in 2008 that is SMART's major funding.

SMART supporters have formed the SMART Riders Coalition, which includes business, labor and non-profit groups and Assemblyman Michael Allen, D-Santa Rosa.

"It is the project we voted for, it is a 70-mile train from Cloverdale to Larkspur, eventually," said Sandra Lupien, outreach director for the Sonoma County Bicycle Coalition, one of the coalition members.

"When we voted for SMART, no one knew about the economic downturn," Lupien said. "The economy changed quite a bit. Any reasonable person would expect a public works project the scope of SMART to be affected."

SMART has a $360 million plan to open an initial segment from Railroad Square in Santa Rosa to downtown San Rafael, with plans to extend the line to Cloverdale and to Larkspur as additional funding becomes available.

The start of SMART train service, scheduled to begin in the fall of 2014, is now likely to be delayed to 2015 or 2016, according to SMART officials.

The organizations behind the formation of the coalition were the Friends of SMART and the Sonoma County Transportation and Land Use Coalition, a conservation group.

There are now 17 groups that are members of the SMART Riders Coalition, which represent environmentalists, labor and transportation advocates.

Speakers at the rally will include Sonoma County Supervisor Shirlee Zane, a member of the SMART board, representatives of the North Bay Central Labor Council, Friends of SMART, Operating Engineers Local 3, the Sonoma County Bicycle Coalition, the Accountable Development Coalition and the Living Wage Coalition of Sonoma County.

The rally also will feature old-time railroad tunes by Rosie and the Railroaders.