California lawmakers neared a crucial vote Friday to determine the fate of an ambitious plan for connecting Los Angeles and San Francisco with the nation's first dedicated high-speed rail line. The bill backed by Gov. Jerry Brown authorizes building the first stretch in the agriculturally rich Central Valley. It faces a tight vote in the state Senate, with some Democrats skeptical the $68 billion project will ever be completed. "This is a big vote," Senate President Pro Tem Darrell Steinberg said as the bill was brought up for debate. "In the era of term limits, how many chances do we have to vote for something this important and long-lasting?" Dan Richard, chairman of the California High-Speed Rail Authority, which is managing the project, said California will lose billions of dollars in federal aid -- essentially killing the bullet train -- if the Senate fails to pass the bill before adjourning Friday for a monthlong recess. Richard said California entered a contract that called for the federal government to provide money for building the Central Valley segment if the state also put up its share. "Last week, the Department of Transportation reiterated that `we expect California to deliver the project that it said it was going to deliver if we gave you the money,"' Richard said Thursday. If the Obama administration rescinds the grant, the state won't have enough money to build the first segment on its own. The bill, SB1029, easily passed the Assembly on Thursday. It would allow the state to begin selling $2.6 billion in voter-approved bonds to finance the first 130 miles of track from Madera to Bakersfield. The federal government has agreed to chip in $3.2 billion for a total of nearly $6 billion to build the initial segment. California was able to secure more federal aid than expected after Florida, Ohio and Wisconsin turned down money. No Republicans were expected to support the project, so the bill needs support from 21 of the 25 Democratic senators to pass with a majority in the 40-member chamber. At least half a dozen Democratic lawmakers remained opposed, skeptical or uncommitted. Some are concerned about how the vote will impact their political futures, while others were wary about financing and management of the massive project. One dissenter, Sen. Joe Simitian, D-Palo Alto, said public support has waned for the project, and there are too many questions about financing to complete it. It's not a choice between jobs or no jobs, but whether the state implements the right rail plan, he said. "Is there additional commitment of federal funds? There is not. Is there additional commitment of private funding? There is not. Is there a dedicated funding source that we can look to in the coming years? There is not," Simitian said. In recent days, Democratic leaders included more funding to improve existing rail systems in an effort to entice support for the bullet train. The bill now allocates a total of $1.9 billion in bonds for regional rail improvements in Northern and Southern California. The upgrades include electrifying Caltrain, a San Jose-San Francisco commuter line, and improving Metrolink commuter lines in Southern California. Brown, a Democrat, is pushing for the massive infrastructure project to accommodate expected population growth in the nation's most populous state, which now has 37 million people. He has joined legislative leaders and labor groups in saying the project is sorely needed to create jobs in a region with higher-than-average unemployment. Steinberg, the Senate majority leader, said passing the bill means, "Californians will be glad that we made the decision and they have a 21st century modern transportation system that will be the pride of the country and the pride of the world." Critics say the project is too expensive and unnecessary. "I believe this is a colossal fiscal train wreck for California," said Sen. Tony Strickland, R-Thousand Oaks.