Facing a Friday deadline to turn in petitions, opponents of a Sonoma-Marin Area Rail Transit train are still not sure if they will be able to force an election to repeal the SMART sales tax.

"I don't know if we have enough signatures," said Clay Mitchell of Windsor, co-chairman of RepealSMART. "I think we are close. Beyond that at this point, I don't know."

Mitchell said backers of the petition drive plan to turn in petitions to the registrars of voters in Sonoma and Marin counties on Friday, if they believe they have 15,000 valid signatures.

They argue the threshold is 15,000 signatures, citing Proposition 218, a 1996 initiative requiring voter approval of tax increases.

However, SMART officials believe it is 39,000 signatures, the threshold set in an elections code cited by the Secretary of State.

RepealSMART has been collecting signatures since late September in an attempt to put a measure on the November ballot to overturn Measure Q, a quarter-cent sales tax passed by voters in November 2008.

After the Friday deadline to turn in petitions, the registrars have 30 working days to validate the signatures.

The sales tax is the major source of funding for the planned commute trains between the two counties.

RepealSMART contends that SMART's plan, which would open with trains running between Guerneville Road in Santa Rosa and downtown San Rafael in late 2015 or early 2016, is far short of what voters approved.

SMART initially planned to have trains running between Cloverdale and Larkspur in late 2014, but the project has been hampered by the weak economy and falling sales taxes, which cut into the money SMART has for construction.

The transit district still plans to extend the line towards Cloverdale and Larkspur as other funds become available.

RepealSMART has stepped up its efforts in the past month and began paying professional signature gatherers $1 per signature.

That spurred the SMART Riders Coalition, which supports SMART, to begin its own campaign three weeks ago, sending people out to distribute pro-SMART leaflets where the signatures were being gathered.

The coalition is made up of labor, business, transportation and conservation groups.

Mitchell said that the coalition members caused problems and hindered the anti-SMART campaign's ability to collect signatures.

Dennis Rosatti of Sonoma County Conservation Action, a member of the coalition, said members passed out pro-SMART leaflets to people coming in and out of stores, but did not confront or stand in front of those gathering the signatures.

"It has been pretty cordial, especially with the volunteer signature gatherers," Rosatti said. "The paid folks, they are typically carrying multiple petitions for state initiatives. They are a bit more aggressive, from what we have discovered."

You can reach Staff Writer Bob Norberg at 521-5206 or bob.norberg@