SACRAMENTO – If voters reject Gov. Arnold Schwarzenegger's $15 billion fiscal-recovery bond measure in March, his administration said yesterday, a backup bond plan would be smaller than originally thought and would leave a larger budget gap.

The governor's top budget aide, Donna Arduin, notified legislators yesterday that the amount of the backup bond, if it survives a court challenge, would drop from $10.7 billion to $8.6 billion.

Arduin said the amount of the bond is determined by the deficit at the end of the fiscal year last June, and the deficit has recently been recalculated to be about $2 billion smaller because of unanticipated tax revenue and new spending figures.

"Based on the latest available data, the accumulated deficit would now be certified at $8.6 billion," Arduin said in a letter to legislative fiscal committees.

The governor is mounting a full-scale campaign for passage of Proposition 57, the $15 billion fiscal-recovery bond measure, and a companion balanced-budget amendment, Proposition 58.

Schwarzenegger, a Republican, and Democratic state Controller Steve Westly held a third in a series of rallies for the ballot measures yesterday at a retirement community in Walnut Creek.

A similar rally has been tentatively scheduled for San Diego on Tuesday.

The two ballot measures, trailing in polls taken this month, are linked, and one cannot take effect without passage of the other.

"We are not borrowing new money," Schwarzenegger said yesterday. "We are refinancing inherited debt."

The current state budget signed by former Gov. Gray Davis, who was replaced by Schwarzenegger in the October recall election, was balanced with $10.7 billion in bonds. But those bonds are being challenged in court because they were not approved by voters.

Schwarzenegger is seeking voter approval of the new bond package to avoid the risk of court rejection. The amount of his bond measure, $15 billion, reflects Arduin's previous estimate of the inherited debt at the end of the current fiscal year on June 30.

If voters reject the governor's bond measure, Arduin said that relying on the earlier, "Plan B" bonds would add about $5 billion to the budget gap because of borrowing costs and other factors.