SF, LA police unions target SF DA Gascón in letter to Gov. Brown

District Attorney George Gascon leaves a news conference after announcing he is filing felony charges against two Alameda County Sheriff's deputies in San Francisco, Calif. on Tuesday, May 10, 2016. Sheriff's deputies Luis Santamaria and Paul Wieber are accused of beating Stanislav Petrov leaving him seriously injured in a San Francisco alley in November 2015. less District Attorney George Gascon leaves a news conference after announcing he is filing felony charges against two Alameda County Sheriff's deputies in San Francisco, Calif. on Tuesday, May 10, 2016. Sheriff's ... more Photo: Paul Chinn, The Chronicle Buy photo Photo: Paul Chinn, The Chronicle Image 1 of / 1 Caption Close SF, LA police unions target SF DA Gascón in letter to Gov. Brown 1 / 1 Back to Gallery

Police union officials took another shot Wednesday at their longtime nemesis, San Francisco District Attorney George Gascón, this time in a letter sent to Gov. Jerry Brown asking that he not appoint a “failed prosecutor” to replace U.S. Sen.-elect Kamala Harris as state attorney general.

Gascón, whose push to reform the police force has been met with stiff resistance, has been mentioned as a possible candidate for attorney general, but could not immediately be reached for comment Wednesday. In the past, he has said he had no plans to run for the job.

Martin Halloran, president of the San Francisco Police Officers Association, penned this week’s letter jointly with Craig Lally, the head of the Los Angeles Police Protective League, saying that Gascón has a “poisonous relationship with law enforcement” and is “a reckless and erratic man with bad judgment.”

“To appoint him to higher office would endanger public safety,” the letter reads. “Gascón’s actions have proven that he is a shameless opportunist.”

The letter lists many of the same gripes that arose after Gascón began his aggressive push to reform the city force that he once led as chief — in particular after he assembled a panel of retired judges to investigate systemic bias in the department following the first of two racist text-messaging scandals.

In his testimony in front of the panel, Gascón lambasted the police union and the existence of what he called an “old boys club” mentality within the department.

Halloran and Lally — who was one of the Christopher Commission’s 44 “problem officers” named in the aftermath of the police beating of Rodney King — also picked at Gascón’s record as a prosecutor, calling him an “inexperienced lawyer.” The union leaders criticized his felony filings, saying his office oversaw a steep decline from 2010 to 2015.

Gascón has advocated for changes in the criminal justice system that seek to reduce incarceration.

Vivian Ho is a San Francisco Chronicle staff writer. Email: vho@sfchronicle.com Twitter: @Vivian Ho