Bill Cosby To Alleged 15-Year-Old Victim ... You Extorted Me In Bogus Lawsuit

Bill Cosby is lashing out at the woman who claims he got her drunk and then sexually assaulted her at the Playboy Mansion in 1974 ... saying she's a liar who tried extorting him and raising the price as new women came forward.

Cosby just filed legal docs -- obtained by TMZ -- in which he says Judy Huth's lawyer approached his attorney, Marty Singer, last month and made "ominous references to criminal penalties." The docs say Huth's lawyer demanded $100K for silence, and later increased the demand to $250K as more women came forward.

In the new docs, Cosby notes the woman -- who is now 56 years old -- tried to sell the story to the tabloids around 10 years ago but no one bit. So the comedian says it's total BS that she would now say she had a repressed memory, which would allow her to file a civil lawsuit. In other words, she'd have to file suit within 3 years of the time she remembered, but she supposedly remembered a decade ago.

The docs say her story falls apart because she claims she and Cosby played a "drinking game" 40 years ago ... yet Cosby is "a life-long non-drinker."

The docs also say Huth's lawyer was sketchy when he tried squeezing money out of Cosby, not even knowing if Huth went to a therapist.

Cosby is demanding that the lawsuit get dismissed, and he wants monetary sanctions as well.