In the Democrat stronghold of California, Arnold Schwarzenegger is the most popular governor in 13 years. His 65 percent approval rating is double that of the Democrat-run Legislature, according to a new poll by Field Research Corp. "He's certainly got a lot of political capital stored up with the voters," said pollster Mark DiCamillo. Schwarzenegger is California's favorite guv since George Deukmejian, also a Republican. His popularity peaked at 72 percent in 1985, according to Field.