SAN FRANCISCO (KCBS) – New polling found a slim majority of California voters favor the tax-hike initiative the governor placed on the November ballot.

51 percent of likely California voters participating in a Field Poll released Thursday said they back Proposition 30, while 38 percent oppose it. Thirteen percent remain undecided.

“The governor’s proposal is still ahead, but I would say it’s not ahead by any comfortable margin,” said Field Poll director Mark DiCamillo.

KCBS’ Barbara Taylor Reports:

Prop 30 would raise the sales tax, and also raise the income tax for the wealthy. A rival tax initiative to fund schools, Proposition 38, remains below the critical 50 percent threshold.

An initiative by civil rights attorney Molly Munger, Proposition 38 would raise income taxes on all but the poorest earners with the money going directly to school districts rather than through the state.

“Voters are coming to the realization that there are these two competing measures on the ballot,” DiCamillo said. “So it’s giving some of them pause.”

A separate survey by the Public Policy Institute of California poll released Wednesday found the governor’s Prop 30 had support from 52 percent of likely voters with 40 percent opposed.

Both surveys also indicate that support has fallen slightly since mid-summer. Even so, Brown’s tax campaign remained optimistic, calling support for the tax increase “strong and steady.”

A University of Southern California Poll in August found slightly higher support at 55 percent for the Brown measure.

DiCamillo said an advertising blitz during the final six weeks of the campaign could prove decisive on a measure whose support is strongest among minority and low-income voters.

Field and the Institute of Governmental Studies at the University of California, Berkeley jointly interviewed 1,183 registered California voters by telephone from Sept. 6-18. The poll has a sampling error margin of plus or minus 4.8 percentage points for the 902 likely voters surveyed.

(Copyright 2012 by CBS San Francisco. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed.)