LOS ANGELES (Reuters) - The Los Angeles County Sheriff's Department is edging closer to court oversight of its jail system after the U.S. Department of Justice found mentally ill inmates were mishandled in vermin-infested facilities where suicides are too common.

Justice Department attorneys warned county officials in a letter last week that they would seek a court-enforced consent decree to resolve problems with the jail system, according to a copy of the letter obtained by Reuters.

Los Angeles County Assistant Sheriff Terri McDonald confirmed in a statement that "active negotiations" were underway with the Justice Department but said it was premature to discuss specifics.

A consent decree would strip local officials of many powers in running the county's inmate facilities and mark the culmination of over 12 years of federal monitoring of the country's largest jail system.

Federal officials probing the jail system have found that treatment of mentally ill inmates violates their constitutional rights.

Prisoners are not properly checked to prevent suicides and living conditions are "dimly lit, vermin-infested, noisy, unsanitary, cramped and crowded," especially at Men's Central Jail in downtown Los Angeles, federal officials told county officials in a letter in June.

Suicides in the jail system, which has about 19,000 inmates spread across a half-dozen facilities, skyrocketed from four in 2012 to 10 the following year, many of them preventable, federal officials said in the June letter.

Federal officials who have monitored the county jail system since 2002 said in their letter dated Sept. 25 that they would provide county officials with the proposed terms of a consent-decree before a meeting scheduled for this past Thursday.

Those proposed terms have not been publicly released, and a county spokesman, David Sommers, declined by email to provide details on the discussions. A Justice Department spokeswoman also declined comment.

A separate federal probe into prisoner abuse and other misconduct inside the Los Angeles County jail system has already led to the conviction of seven current and former sheriff's deputies for trying to thwart the investigation.

Earlier this year, Los Angeles County Sheriff Lee Baca resigned after 16 years leading the department, and one of two candidates running to replace him, former Undersheriff Paul Tanaka, has been criticized for his oversight of the jails.

(Reporting by Alex Dobuzinskis; Editing by Eric Beech)