Two factions of attorneys fighting for the same cause are now embroiled in a power struggle in one of the nation’s biggest product liability battles — over the diet drug combination fen-phen.

The contentious mood that has settled over the two camps could, at the very least, put an end to some state court claims and might even derail the multibillion-dollar settlement reached with the makers of the weight-loss drug. At the center of the debate is whether all fen-phen users who are part of class-action litigation in Florida and numerous other states should be forced to accept a deal hammered out last October by American Home Products, manufacturer of the drug. “There is disagreement among the bar as to whether the settlement is acceptable,” said Karen Cohen, a Miami attorney who is litigating a handful of fen-phen cases. “I don’t think it’s an adequate settlement.”