Lawyers representing Alan Dershowitz filed a legal letter Friday indicating they’re planning a countersuit against Jeffrey Epstein’s “sex slave” Virginia Giuffre for defamation.

The move comes after a Manhattan federal judge ruled Giuffre can move forward with her defamation lawsuit against Dershowitz — but that she’ll have to find new representation. (She was repped by David Boies, but Dershowitz intends to call lawyers from Boies’ firm as witnesses in his case.)

A letter from Dershowitz’s lawyers at Aidala, Bertuna & Kamins to Judge Loretta Preska filed Friday requested an adjournment of a discovery conference in the case until Dec. 2, but also revealed: “In the interim, Mr. Dershowitz will file his answer to the plaintiff’s complaint and assert counterclaims for defamation and other tortious conduct against plaintiff seeking substantial damages.”

The letter said the adjournment is requested because his lawyers Arthur Aidala and Imran Ansari will be traveling during a scheduled Nov. 20 hearing — but would also “allow plaintiff to confer with her new counsel about the full scope of this case, and will allow counsel for both parties to confer more meaningfully.”

Aidala commented further, “We can now file a counterclaim. We are moving forward emboldened … [Dershowitz] has been fighting these charges since the first time they were levied against him … Our next step is — we’ve been on defense, and now we’re going on offense, with all the tools and talents we have before us to clear Mr. Dershowitz’s good name.”

Dershowitz told us he’ll invite the FBI to his trial. “The goal is simple: to have the truth come out. I have nothing to hide,” he said.

He’s publishing a book, “Guilt by Accusation: The Challenge of Proving Innocence in the Age of #MeToo,” on Nov. 19.

Giuffre alleged she was “lent out” to famed attorney Dershowitz for sex by the late Epstein. She sued in April after Dershowitz publicly denounced her allegations as untrue.