Former Rep. Richard Pombo (R-Calif.) will run for the seat being vacated by Rep. George Radanovich (R-Calif.) in 2010, adding more firepower to what is expected to be a hotly contested GOP primary.Pombo, who was defeated for re-election in 2006, is expected to make the announcement Tuesday. He contacted Rep. Devin Nunes (R-Calif.) to tell him of his decision, Nunes’ chief of staff, Johnny Amaral, confirmed. Pombo is the third Republican to throw his hat into the ring since Radanovich announced last week that he is retiring in 2010, citing his wife’s health issues. Radanovich, who is serving his eighth term, endorsed state Sen. Jeff Denham (R) as his chosen successor. And former Fresno Mayor Jim Patterson (R), who had been considering a primary challenge to Radanovich, also told local news outlets that he is running.Pombo’s candidacy is likely to split the California Republican delegation. Denham is well-regarded in state and national GOP circles and has the strong backing of Radanovich, but Pombo also has close ties with a number of Members from his 14 years in Congress.Amaral said that Nunes and Pombo remain close and that he couldn’t “imagine a scenario— where the Congressman doesn’t endorse his former colleague.Patterson, meanwhile, has the geographic edge, hailing from the district’s largest city, Fresno. Neither Pombo nor Denham live in the district.More candidates are likely to emerge in the GOP field. Another Republican name being mentioned for the seat is Fresno City Councilman Larry Westerlund.Democrats do not have an obvious top-tier challenger in the heavily Republican-leaning district. However, they would likely welcome the chance to go up against Pombo, whose ethics controversies, including ties to disgraced lobbyist Jack Abramoff, contributed to his 2006 loss to now-Rep. Jerry McNerney (D) in the nearby 11th district.