A North Bay business group Wednesday called on opponents of the SMART commute train to abandon the repeal campaign, saying their own poll had found majority support for the Sonoma-Marin rail line.

But the organization collecting signatures in a bid to put the repeal on the ballot challenged the survey as biased.

The poll, conducted for the North Bay Leadership Council in late October, showed that 58 percent of registered voters in Sonoma and Marin counties oppose repealing the quarter percent sales tax. Another 32 percent supported a repeal and 10 percent are undecided.

"SMART has been battered and a lot of negative things said the past three years, but it has held strong, people are pretty unshakable in their support," said Cynthia Murray, president and chief executive officer of the council. It represents 40 large employers in Sonoma and Marin counties.

Murray would not release the poll data nor the questions that were asked. She said only that the questions dealt with the issues that have been raised by SMART's opponents.

The poll results were challenged by John Parnell of Novato, co-chairman of RepealSMART.

"You can make the poll say anything you want, based on the questions," Parnell said.

RepealSMART has been collecting signatures since September in an effort to qualify a measure for the June or November ballot to repeal the quarter-cent sales tax.

The tax, which is SMART's major financial support, was adopted by voters in Sonoma and Marin counties in 2008, with more than 70 percent in favor. Passage required two-thirds approval.

The poll was conducted by Dresner Wickers/Barber Sanders, a San Francisco political consulting firm, Oct. 27 to 30 in telephone interviews with 501 registered voters in Sonoma and Marin counties. It has a margin of error of 4.37 percent.

SMART has a $360 million plan to build a rail line from Railroad Square in Santa Rosa to downtown San Rafael, extending the line to Cloverdale and to Larkspur if additional funds become available.

It is also likely that SMART will be delayed in beginning service one or two years past the fall 2014 scheduled start-up date.

SMART's critics contend that is not what voters approved in November 2008, don't believe there will be additional funds available to extend the line and feel voters should have another chance to vote on the tax.

Murray said the North Bay Leadership Council still supports SMART because it will offer a transportation alternative to Highway 101 and will create jobs and boost the economy.

"It is obvious we need an alternative to 101 and SMART is the only viable choice," Murray said. "There is tremendous support for having green transportation alternatives, to not be dependent on cars and oil and people are looking for ways to get out of their cars."