By Phoenix Tso

LOS ANGELES (Reuters) - Former Los Angeles County Sheriff Lee Baca on Monday withdrew his guilty plea to a charge of lying to investigators, opting instead to face trial in a corruption case that clouded his final years as chief custodian of the nation's largest jail system.

Baca, 74, was permitted to back out of his plea deal after a federal judge ruled two weeks ago that a six-month prison term recommended by prosecutors as part of the agreement - far less than the five-year maximum penalty - was too lenient.

Both prosecutors and defense lawyers have cited Baca's recent Alzheimer's disease diagnosis in their reasoning for a seeking a relatively light sentence.

U.S. District Judge Percy Anderson gave Baca and prosecutors time during a court recess on Monday to negotiate an alternative he might find acceptable, but the two sides failed to come to terms during three hours of talks.

"While my future and my ability to defend myself depend on my Alzheimer's disease, I need to set the record straight about me and the Los Angeles County Sheriff's Department on the misleading aspects of the federal investigation while I am capable of doing so," Baca said in a brief statement he read to reporters outside the courthouse.

Defense lawyer Michael Zweiback said his client was ready to agree to a prison term of up to a year but unwilling to stand by his guilty plea without an indication from the judge as to whether Anderson would find 12 months satisfactory.

Dressed in a gray, pin-striped suit and pink tie, Baca appeared healthy and showed no outward signs of impairment, though Zweiback said earlier that Baca's disease was reaching an "advanced" stage.

Anderson set a trial date for Sept. 20.

Baca served as the top elected law enforcement official in Los Angeles for 15 years before retiring in January 2014 amid a federal investigation of inmate abuse and other wrongdoing, including cover-up attempts, at two downtown lockups.

He pleaded guilty in February to a charge of making false statements to investigators when he asserted in 2013 that he had no prior knowledge of his deputies' efforts to harass a Federal Bureau of Investigations agent and thwart a criminal probe of his department.

Specifically, Baca admitted he actually was aware that his deputies planned to intimidate the agent and that he had directed them to "do everything but put handcuffs" on her, his plea agreement stated.

Seventeen others from the sheriff's department have been convicted of criminal charges for misconduct inside the Los Angeles County jail system, the nation's largest with an inmate population of about 18,000.

Baca's former second-in-command was sentenced to five years in prison in June after being found guilty of conspiracy and obstruction of justice.

(Writing and additional reporting by Steve Gorman in Los Angeles; Editing by Leslie Adler and Jonathan Oatis)