SACRAMENTO – Rejecting what he sees as a piecemeal approach to school reform, Gov. Arnold Schwarzenegger has sent back legislation that would have granted districts limited flexibility in setting student-teacher ratios in kindergarten through third grade.

The governor's move drew cautious responses from school officials who have long pursued modifications to a popular class-size reduction program. They have argued that rigid rules increase costs, tie up space and faculty, and escalate tension as veteran teachers joust over coveted assignments to lower grades.

"At least it's not a veto," said Rick Pratt, assistant executive director of the California School Boards Association. "The door is open for us to go back."

San Diego Unified School District trustees endorsed the measure, said Miles Durfee, who monitors legislation for the district.

"We were hopeful he would sign it as a first step and direct the Legislature to come back with more substantial flexibility," Durfee said.

The district has no plans to abandon smaller class sizes regardless of the fate of future measures, Durfee said.

In the Poway Unified School District, superintendent Donald Phillips said he is optimistic that Schwarzenegger can be won over.

"I don't think we're disheartened at this point," said Phillips, whose district has pushed several variations of class-size bills.

No decision has been made, but the Poway district is studying whether it can afford to keep kindergarten classes small. The district remains committed to a 20-1 ratio in the other grades, Phillips said.

Schwarzenegger asked Sen. Byron Sher, D-Pal Alto, to withdraw his SB 311 so lawmakers can focus on a comprehensive package granting districts more say over running $2 billion worth of various categorical programs, such as bilingual teacher training, transportation and dropout prevention. The bill passed the Legislature earlier this month.

Ashley Snee, a spokeswoman for the governor, said Schwarzenegger is not unilaterally opposed to changing class-size enrollment rules. But, reforms to provide flexibility cannot be done "piece by piece," she said.

The program, which limits K-3 class sizes to 20, is voluntary. To encourage participation, the state pays $906 per student as an incentive. However, districts lose funding if a classroom exceeds the cap.