Bishop Daniel Walsh of the Santa Rosa diocese said in a one-page statement to parishioners he put "caution" before "doing the right thing" in handling the allegations against priest Xavier Ochoa.
Church officials say Ochoa admitted April 28 to sexually abusing a 12-year-old altar boy, but the allegations were not reported to Child Protective Services until May 1, and Ochoa disappeared the next day.
"I made an error in judgment by waiting to report Rev. Ochoa's admission," Walsh wrote in the statement, distributed at Saturday Mass throughout the diocese, which stretches from Santa Rosa to the Oregon border. "I should have acted immediately, and not delayed. For this I am deeply sorry."
Ochoa, 68, was charged June 22 with 10 felony counts and one misdemeanor count of child sex abuse involving three alleged victims. A warrant was issued for his arrest.
Walsh said the public admission could aid prosecutors in filing criminal charges against him.
Prosecutors said in July they were investigating whether church officials violated a state law requiring doctors, nurses, teachers and clergy members to immediately report child sex abuse claims.
"If I am found guilty for not taking immediate action, I will accept whatever punishment is imposed," Walsh said.
Sonoma County District Attorney Stephan Passalacqua told The (Santa Rosa) Press Democrat on Saturday he had not seen the letter and that the investigation was still pending.
Walsh said he lamented the damage his delayed reporting caused the church and wanted to admit his error.
"With this letter," he wrote, "I am choosing to step forward and admit my mistake because not to do so would only compound my original inaction and further tarnish all of our shared efforts over the past six years, in working to eradicate sexual abuse in the Church."