Hounded by scandal and criticism over the last several years, Sheriff Lee Baca is expected Tuesday to announce his retirement after 15 years of leading the largest sheriff’s department in the country.

A source, who asked to remain anonymous, said Baca notified county officials late Monday.

Baca’s spokesman did not immediately return calls seeking comment, but a press conference is scheduled for 10 a.m. Tuesday at department headquarters in Monterey Park.

Baca, 71, was first elected in 1998, after Sheriff Sherman Block — his mentor before becoming his rival — died unexpectedly. He has trounced every other candidate since. Next year’s election, however, might have been different.

Last month, the FBI arrested 18 sheriff’s deputies, sergeants and lieutenants on various acts of misconduct, including beating visitors, putting handcuffs on an Austrian consular official without justification, threatening an FBI agent at her home and hiding an FBI informant.

Under his watch, the department was also accused of harassing minorities in Lancaster and Palmdale.

A federal jury held Baca personally liable for $100,000 after deputies broke several bones on an inmate during one jail beating.

Early in 2012, the American Civil Liberties Union filed a class action lawsuit against Baca, accusing him of condoning a pattern of deputies using excessive force on inmates. Later that year, the Commission on Jail Violence criticized his “failure of leadership,” saying he “did not pay attention to the jails.”

Baca had raised at least $240,000 for his reelection campaign. He was supposed to face off against former second in command Paul Tanaka, former jail commander Robert Olmsted, retired sheriff’s Lt. Patrick Gomez and Los Angeles Police Department officer Lou Vince.

Olmsted said Tuesday that Baca’s retirement was “inevitable.”

“It’s something that I had anticipated needed to occur,” he said. “I did think it would be a bit further down the road, but his retirement is best for the department and best for the citizens of LA county.”

“It’s absolutely critical that he step down, what with all the investigations, corruption and mismanagement that have occurred,” Olmsted added

In an interview with ABC7 last year, Tanaka linked Baca to the attempt to hide the FBI informant in Men’s Central Jail.

“(Baca) said, ‘I want you to make sure that thing is locked up, and that thing is not going anywhere. Period,’ ” Tanaka said. “And ‘I want that inmate interviewed, and I don’t want him to go anywhere.’ ”

Among Baca’s accomplishments are bringing crime down to its lowest level in 40 years and creating the Education-Based Incarceration Program, which has allowed 7,000 inmates to take academic and vocational courses while behind bars, so they can obtain the skills and jobs needed to help them avoid going back to jail.