LILLE, France (Reuters) - Dominique Strauss-Kahn, the former International Monetary Fund (IMF) chief who was tipped to become French president before being accused of sexual assault by a New York maid in 2011, will testify to a criminal court on Tuesday over his alleged role in sex parties with prostitutes.

The allegations that he participated in a French sex ring have dogged the once prominent Socialist ever since criminal charges were dropped against him in the New York case and he settled a civil case with chambermaid Nafissatou Diallo.

Strauss-Kahn, 65, is accused of instigating parties he knew involved prostitutes between 2008-2011 in the northern French city of Lille, Brussels, Paris and Washington D.C.

Strauss-Kahn's lawyers acknowledge their client took part in the parties, but say he did not know the women were prostitutes and so reject the charge against him of pimping, or "procuring with aggravating circumstances".

Investigating magistrates say that charge applies because in France it covers any activity seen as facilitating prostitution. In Strauss-Kahn's case, it is alleged that he allowed his rented apartment to be used for sex parties involving prostitutes and that the parties were organised for his benefit.

Moreover, because he did not pay them himself, he is alleged to have received benefit in kind from prostitution.

Strauss-Kahn, who says his political career is over, risks as much as 10 years in prison and a fine of up to 1.5 million euros (S$2.3 million) if convicted.

The three-week trial began last week. Strauss-Kahn is expected to respond on Tuesday for the first time to the testimony of two former prostitutes who say they participated in the parties.

Fourteen people, including Strauss-Kahn, are defendants in the "Carlton Affair" trial, so named after the hotel in Lille that sparked the investigation into a sex ring.

The accusations made against Strauss-Kahn by the New York maid in 2011 made it impossible for him to run on the Socialist ticket for the presidential election in the following year. That allowed Mr Francois Hollande to come forward and beat conservative incumbent Nicolas Sarkozy.

Strauss-Kahn served as French finance minister in the late 1990s. He then became one of the world's most influential decision-makers in 2007 as head of the IMF, a public lender that plays a central role worldwide in the rescue of failing economies.

That high-flying career ended in May 2011 when he was escorted handcuffed into custody in New York following Ms Diallo's accusations.