By Dan Whitcomb

LOS ANGELES (Reuters) - Three months into the worst oil spill in U.S. history, most Californians oppose offshore drilling, marking a strong shift in opinion on the issue, a poll has found.

Some 59 percent of residents say they are against drilling for oil off the state's coastline while 36 percent are in favor, according to the Public Policy Institute of California survey released on Wednesday.

Last year the same poll showed 43 percent were opposed to offshore drilling and 51 percent approved.

The poll was released more than 100 days into BP Plc's Gulf of Mexico oil spill, as BP prepares to start its latest effort to plug the gusher, called a "static kill," pumping drilling-mud and cement into its blown-out well.

The survey also found 67 percent support a California law to cut greenhouse gas emissions to 1990 levels within the next 10 years. A November ballot initiative, AB 32, seeks to suspend it while the state battles tough economic times and double-digit unemployment.

"After consistently opposing more offshore oil drilling, residents began to waver as gas prices increased," PPIC CEO Mark Baldassare said. "But events in the Gulf appear to have renewed opposition to more drilling here.

"In contrast, the lingering effect of the recession and a continuing state budget crisis haven't changed Californians' overall view of AB 32," he said.

The poll's findings were based on a telephone survey of 2,502 Californians between July 6 and July 20. The overall margin of error was plus or minus 2 percentage points.

The worst U.S. oil spill followed the April 20 explosion and fire on Transocean Ltd's drilling rig Deepwater Horizon licensed to BP Plc.

(Editing by Xavier Briand)