SAN JOSE, Calif. -- A measure that would bring Bay Area Rapid Transit to the South Bay is now ahead by the slimmest of margins, according to the latest election results released by the Santa Clara County Registrar of Voters.

Results released Monday show 407,932 votes in favor of Measure B and 203,954 against. The measure would authorize a one-eighth-cent sales tax to fund the 16-mile BART extension.

The latest figures give Measure B a 66.67 percent majority, or two-thirds, which is what it requires to pass. However, with about 9,800 ballots left to count, final results could swing either way.

The BART expansion would run from Fremont through Milpitas, San Jose and Santa Clara, adding six stops to the line. The $6.1 billion project would also connect BART with Caltrain, the Altamont Commuter Express, Santa Clara Valley Transportation Authority lines and Amtrak.

The one-eighth-cent sales tax proposed in the initiative comes out to around $13 a year per resident, proponents said.

If Measure B passes, the tax will only be collected if state and federal funding is also in place. The tax would be in effect for 30 years and construction would begin in 2013 and end in 2017, according to the county.

Measure B campaign spokesman Phil Yost said today proponents of the BART expansion are hoping to maintain the momentum gained in the last week.

"We're happy," he said. "We're ahead by this tiny, tiny margin."

Yost said the recently counted batch of provisional ballots has strongly favored Measure B. He pointed out that the measure will pass if two-thirds of the remaining, uncounted votes favor the BART expansion.

Registrar of Voters spokeswoman Elma Rosas said the bulk of the 9,800 uncounted ballots are provisional. About 5,000 ballots were counted from the time results were released Friday afternoon and the time results released were Monday, she said.

She said about 98 percent of all ballots cast Nov. 4 should be counted by Friday, with about 2 percent to be counted in the time before results must be certified on Dec. 2.

"We will meet the deadline," Rosas said.

Rosas said while some races are closer than others, nothing will be official until every vote is counted.

Elections officials will post updated Election Day results Monday, Wednesday and Friday afternoons online at http://www.sccgov.org/elections/results/nov2008/.