Banks being probed over alleged interest-rate manipulation scored a big victory in their battle against scores of private lawsuits seeking billions of dollars in potential damages.

A federal-court judge on Friday agreed to dismiss claims that the 16 banks targeted by the suits broke federal antitrust laws through alleged suppression of the London interbank offered rate, or Libor.

In a 161-page ruling on the banks' motions to dismiss the leading suits seeking class-action status, U.S. District Judge Naomi Reice Buchwald allowed some of the claims to proceed, including allegations the banks breached commodities laws.

But if her ruling stands, it would take out a central plank of the litigation. The federal antitrust claims that the judge threw out can pay up to triple damages.

Unless the plaintiffs can prevail on appeal, Friday's ruling on the antitrust claims would significantly reduce the potential cost to the banks. The ruling also is likely to reduce the financial inventive for new plaintiffs to join investors, cities, lenders and other parties that have already filed lawsuits.