LOS ANGELES — Competition between Senator John McCain and Mitt Romney for California’s vast array of Republican delegates was heating up on Thursday, with Mr. McCain poised to receive a major endorsement and Mr. Romney preparing to broadcast television advertisements in California and several other February 5 states.

Mr. Romney, who has done well with fundraising compared to his rivals, but who also has repeatedly dipped into his own deep pockets, will buy advertising time in California’s expensive media markets Thursday, as well as markets in several other states across the country that are still being chosen, Carl Forti, the Romney campaign’s political director, said on Thursday morning.

Meanwhile, California Governor Arnold Schwarzenegger, who has forged a moderate record and spoken out against partisanship in Washington, is to throw his political brawn behind Mr. McCain Thursday after the pair tour a solar energy company here. The news conference is scheduled for 9:50 a.m. local time.

Both Mr. Romney and Mr. McCain are campaigning in California. But perhaps equally urgent to both candidates now is fundraising, with Mr. Romney scheduled to attend two fundraisers Thursday, one here and the other in Orange County, Calif., and Mr. McCain planning to attend one here.

It is unclear if Mr. McCain, who slightly outspent Mr. Romney in television advertising in the final days of their battle in Florida, will be matching Mr. Romney in the television ad wars in the lead-up to the crush of states that vote on February 5. Mr. McCain’s advisers indicated that they will be relying mostly on their candidate’s knack for getting free media, using news conferences, rallies and interviews, and that television advertising will be modest.