The group aiming to halt the Sonoma-Marin commuter rail project has started collecting signatures on a petition to repeal its funding, a spokesman said Friday.

"This project has changed substantially from what was presented in 2008," said Clay Mitchell, a Windsor resident who represents RepealSMART. "It should come back to voters to see if they still support it."

The group is trying to qualify an initiative that would ask voters to repeal the 2008 ballot measure funding Sonoma-Marin Area Rail Transit with a quarter-cent sales tax.

Since then, the project has met financial setbacks, forcing SMART to reduce the North Bay rail line from 70 to 37 miles. Commute trains originally were scheduled to run from Larkspur to Cloverdale starting in 2014, but initial service now is planned for a shorter San Rafael-to-Santa Rosa segment.

The project also is expected to take longer and cost more than originally planned.

Novato-based RepealSMART hopes to gather more than 40,000 signatures by Jan. 28 to put the repeal measure on the ballot in Marin and Sonoma counties.

If it qualifies, it would go before voters in June or November 2012, Mitchell said.

But the group may need only 15,000 valid signatures to qualify the measure. Election law is unclear on the number required, said Gloria Colter, Sonoma County's assistant registrar of voters.

County attorneys are now researching the question, she said.

The repeal group will have volunteers gathering signatures at supermarkets and other public places in Sonoma and Marin counties, Mitchell said. The initiative will need only a simple majority vote in the two counties to pass, even though the measure authorizing the rail line and tax required two-thirds aproval.

Based on projections of SMART ridership, the funding for commuter rail would be better spent widening Highway 101 through the Novato Narrows, Mitchell said. "The train is going to cost 10 to 20 times as much per person as widening the freeway," he said.

SMART chairwoman Valerie Brown said Friday the repeal effort is misguided. The commuter rail project passed with over two-thirds voter support, she said.

"People said they want rail," Brown said. "We believe it's important for our transportation system."

SMART is committed to the full 70-mile project, she said. It's not unusual for a major transportation project to lack funding for full buildout and require construction in stages, said Brown, a Sonoma County supervisor.

"We've never had a project that had all the money to complete it at the same time," she said.