MANILA, Dec 21 (Reuters) - The Philippine government filed a criminal case in court on Wednesday against a staunch critic of President Rodrigo Duterte, accusing her of trying to sabotage a congressional investigation into her alleged involvement in the drugs trade.

The justice ministry's case against its former head, Senator Leila de Lima, says she deliberately skipped the house inquiry and told her ex-driver and alleged bagman to go into hiding and ignore a legislative summons.

De Lima is among only a few high-profile domestic critics of Duterte's campaign against drugs, which has killed about 6,000 people, roughly a third in police operations. The other deaths are classified as under investigation, many believed to be the work of vigilantes.

Duterte's allies in Congress said de Lima had shown disrespect for the inquiry. The criminal case is built around breaches of an article of the law on legislative summonses.

De Lima once led a Senate investigation into suspected extrajudicial killings during Duterte's drugs crackdown and a similarly bloody campaign he oversaw in Davao City when he was mayor.

But she was ousted by his allies as head of that investigation and just days later came under investigation herself in a congressional inquiry in which witnesses testified to her having a pivotal role in the narcotics trade.

De Lima has denied the accusations and filed a case with the Supreme Court to try to muzzle Duterte and stop him from disparaging her in public and making salacious allegations about her private life.

The tide of opposition to her shows the influence Duterte has gained in his short time as president, and how domestic dissent about his drugs war has gained very little traction.

The killings in the anti-drugs campaign have been condemned widely among the international community.

De Lima on Wednesday said the criminal charges would have no impact on her, or change the fact that people were dying as part of Duterte's war.

"It's saddening and frightening that even high-ranking public figures have swallowed hook, line and sinker the fantasy that the Duterte administration has been weaving: that a single person was single-handedly responsible for the proliferation of drugs in our country," she said in a statement, referring to the accusations against her that she is a drug lord. (Reporting by Manuel Mogato; Editing by Martin Petty, Robert Birsel)

Our Standards: The Thomson Reuters Trust Principles.