In a setback for cable television giant Comcast Corp., a federal appeals court has refused to de-certify a class action antitrust suit brought by consumers who claim the company set out to establish a monopoly in the Philadelphia market.

The suit, Behrend v. Comcast Corp. , alleges that Comcast and its would-be competitors struck a series of deals in which they “swapped” assets and customers so that each company would have “clusters” of markets. Those deals gave Comcast monopoly power, the suit says, because its market share of subscribers in the Philadelphia area increased from 23.9 percent in 1998 to 77.8 percent by 2002.