Gov. Jerry Brown's budget proposal offers little reassurance to California's public schools, community colleges and universities, because their funding hinges on whether voters approve a $6.9 billion tax plan.

Education funding for 2012-13 is tied to a proposal for a half-cent sales-tax hike and increased levies on the wealthy that Brown wants to put on the November ballot.

"There is a lot riding on it," said Paul Hefner, director of communications for the Department of Education. "It's our only chance to turn the tide against all the cuts that happen year after year."

If the tax plan fails, it will trigger $4.8 billion in cuts to K-12 and community colleges, and another $200 million each in cuts to the California State University and University of California systems. Officials warn that the school year would shrink by up to one month and community colleges would have to slash courses, services and teachers. Thousands of students would lose access to Cal Grants, putting higher education even further out of reach.

Education officials and student leaders offered tepid appreciation Friday for the governor's efforts to reinstate some of the funding that lawmakers have siphoned off over recent years.

But tying education funding to a tax plan that some say doesn't have a chance of passing only leaves students and educators uncertain about how much money they would have -- and how much they could lose.

"This will be the second year in a row that we would be on needles and pins over a midyear trigger cut," said Dan Troy, vice chancellor for fiscal policy of the California Community College system. "The uncertainty is very hard to live with."

Schools and universities still are struggling to regain their footing after Brown announced $1 billion in cuts last month. The cuts -- triggered when the state didn't meet revenue projections for the year -- forced a $10 per-unit fee increase at community colleges.

Under Brown's plan, about $440 million of the estimated $4.8 billion in revenue from new taxes would go to community colleges, with the rest slated for K-12. Without the money, community colleges would have to cut back counseling, advising services and course sections, Troy said. Courses already have been cut by as much as 15% at some colleges. Layoffs and salary cuts would also be likely, he said.

Should Brown's tax plan fail, the next round of trigger cuts would come Jan. 1, 2013.

For K-12 school districts that already have the most crowded classrooms in the country and have laid off thousands of employees, the importance of new revenue can't be overstated, officials said.

Without it, Fresno County schools would have to increase already-bulging classes and shorten the school year by as much as four weeks, said county schools Superintendent Larry Powell. He said some schools would be open as few as 160 days, down from 180.

"There's no place left to cut but school days," Powell said. "It's a devastating position to be in."

Powell is one of several education leaders who said they support Brown's tax plan -- and will lobby for its passage -- but don't think voters will be interested.

"How do you go to the public and say, give us more taxes?" Powell asked. "They don't trust the government to do what they say they'll do."

Brown's budget proposal also would shift the cost of busing from the state to districts and reallocate money previously used for class-size reduction.

Piling more kids into classrooms will make classes unmanageable and will exacerbate problems like dropouts and truancy, said Fresno Unified School District trustee Larry Moore. He said the average student-to-teacher ratio in the district's K-3 classes is 30-to-1. A few years ago it was 20-to-1.