Democratic presidential candidate Barack Obama has expanded his lead over Republican John McCain in California to nearly 25 percentage points, a new Field Poll shows.

The nonpartisan, statewide poll shows that 54 percent of the California voters likely to take part in the Nov. 4 election favor Obama, a senator from Illinois, compared with 30 percent for McCain, a senator from Arizona. Four percent favor other candidates, and the remaining 12 percent are undecided.

In May, Obama held a 17-point lead, 52 percent to 35 percent.

A top McCain campaign official said recently that McCain's demonstrated appeal to independent voters gives him a chance in California, where 23 percent of the voters are not affiliated with either of the major political parties.

The Field Poll shows Obama leading among nonpartisan voters and minor-party members 60 percent to 18 percent.

The survey also shows a sizable enthusiasm gap, with 51 percent of the Obama supporters saying they are “very enthusiastic” about their candidate, compared with 17 percent of the McCain supporters.

Although some Democrats regard a pairing of Obama and former rival Hillary Rodham Clinton as a “dream ticket,” more Democratic primary voters in California, 48 percent, think Obama should not select Clinton than think he should, 40 percent.

The Field Poll is based on telephone interviews with 672 likely voters conducted July 8 through Monday. It has a margin of error of 3.9 percentage points.