NEW ORLEANS, July 3 (AP) — Food and Drug Administration approval of a drug label does not clear the manufacturer of claims that its warnings were inadequate, a judge ruled in a decision that could potentially affect thousands of federal suits against Merck over the painkiller Vioxx.

“The F.D.A.’s current view on the question of immunity for prescription drug manufacturers is entirely unpersuasive,” Judge Eldon E. Fallon of Federal District Court wrote in the opinion, handed down Tuesday.

Had Judge Fallon sided with Merck, the drug company could have challenged claims brought by thousands of other plaintiffs who say it is to blame for heart attacks and other cardiovascular problems.

The judge rejected Merck’s attempt to throw out lawsuits brought by two people who began taking Vioxx after April 2002, when the F.D.A. approved a label warning that the drug might increase the chance of such problems.

Russ Herman, a spokesman for the plaintiffs’ lawyers in the federal cases, was unavailable for comment.

Merck is considering an appeal, one of its lawyers, Ted Mayer, said in an e-mailed statement.