Pop the champagne, DSK.

Prosecutors will agree to drop the charges against Dominique Strauss-Kahn — either on his next court date in two weeks or even sooner, according to a top investigator in the case who called the eventual dismissal “a certainty.”

“We all know this case is not sustainable,” the source told The Post exclusively yesterday.

“Her credibility is so bad now, we know we cannot sustain a case with her,” the source said, referring to the Guinean hotel maid who accused Strauss-Kahn of trying to rape her in his plush Midtown hotel suite — shocking charges that got the international banker bounced as head of the IMF and also derailed, at least for now, his bid to become president of France.

“She is not to be believed in anything that comes out of her mouth — which is a shame, because now we may never know what happened in that hotel room,” said the source, who is at the center of the investigation and would speak only on the condition of anonymity.

“Did [Strauss-Kahn] use force? Was there actually a crime? I don’t think we’ll ever know.”

Meanwhile, defense sources described a different scenario, in which DSK admittedly engaged with the maid in a consensual, sex-for-money exchange in his Sofitel suite, with no force involved — and she turned against him only when he stiffed her.

“In the past, guests have left stuff for her,” meaning money, one source close to the defense investigation said last night. “She goes back to look for the money,” and is disappointed, the source said. Also likely irking the maid? “His dismissive nature,” said the source.

Multiple investigators for the defense and prosecution have confirmed that they believe the maid was turning tricks at the hotel, and prosecution sources have even accused her of continuing to “entertain” male visitors while in a DA safehouse.

Meanwhile yesterday, French lawyers for Strauss-Kahn promised to fight back with criminal charges of their own against a French writer who claims he tried to rape her nearly a decade ago.

Tristane Banon has accused the French banker of behaving like a “rutting chimpanzee” and allegedly yanking open her bra and attempting to get into her pants during a 2002 interview. Her lawyers said they plan to press charges against Strauss-Kahn in France today.

But the banker’s legal team in Europe says they’ll file a criminal-slander complaint if Banon makes good on her threat.

The volleys of accusations across the Atlantic come as new details emerge on the collapsing sex case in New York.

For six weeks, the maid told investigators a credible and compelling story about her travails of rape and beatings in escaping Guinea’s violent regime, and about her alleged re-victimization last month by Strauss-Kahn.

“One-hundred-percent consistent,” one top investigator called her first month-and-a-half of statements. “Rock solid,” another top investigator said.

Only eight days ago did the maid’s story fall apart, according to two top investigators on the case, and Manhattan DA Cyrus Vance Jr. made what they termed the courageous decision to inform the defense and agree to release Strauss-Kahn without bail.

Officials realized that for six weeks, ever since the May 14 incident, she had bamboozled some of the best minds in the storied Manhattan DA’s Office, including a trio of seasoned top investigators with a combined 75 years in the business — Joan Illuzzi-Orbon, Ann Prunty and Chief DA Investigator Rob Mooney.

Vance “put his very best, most intelligent people on this — and eventually, we found the truth,” said one top investigator.

Defense lawyer Benjamin Brafman declined to talk about the pending dismissal, or about a meeting set for tomorrow morning between the defense team and Vance.

Additional reporting by Bruce Golding

laura.italiano@nypost.com

