Former Rep. Richard Pombo (R-Calif.) will run for the House seat being vacated by Rep. George Radanovich (R-Calif.) in 2010, adding more firepower to a contested GOP primary.

Pombo, who was defeated for re-election in 2006, is expected to make the announcement tomorrow. 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 in the ring since Radanovich announced last week that he is retiring in 2010, citing his wife’s health issues. Radanovich, who is serving his 8th term, endorsed state Sen. Jeff Denham as his chosen successor.

And former Fresno mayor Jim Patterson (R), who had been considering a primary challenge Radanovich, also told local news outlets he is running.