A federal appeals court ruled today that the New York-New Jersey Port Authority has the power to prevent the Anglo-French Concorde supersonic jetliner from landing at John F. Kennedy International Airport.

However, the court also ordered a district judge to hold hearings on whether the Port Authority's 13-month ban on Concorde landings has been stretched out to the point of being unreasonable.

The ruling by the Second U.S. Circuit Court of Appeals in the seesaw Concorde case was a significant setback to British Airways and Air France, operators of the controversial jetliner, because the decision assured that the issue would drage out in various appellate courts for months. The airlines had hoped to begin operations this months.

The three-judge appeals court today sent to case back to U.S. District Court Judge Milton Pollack, who on May 11 declared unconstitutional the Port Authority's ban against Concorde landings at Kennedy. Pollack, ruling on the narrow issue of federal supremacy over state authorities in landing rights, had said that the Port Authority's March, 1976, decision against a 16-month period of test Iandings here was illegal.

The federal appeals court today ordered Pollack to hold new hearings to determine whether the Port Authority, which operates Kennedy and La Guardia airports, was "justified and reasonable" in ordering the ban.

In its 23-page decision, written by Chief Judge Irving R. Kaufman, the court declared, "We are not deciding whether the SST may land at Kennedy airport . . . but we urged the Port Authority to conclude its study and fix reasonable noise levels with dispatch."

A number of communities adjoining Kennedy had charged in civil actions that the SST would create intolerable noise levels. Some community groups have staged demonstrations against the Concorde, hoping to close down the airport.

The effect of the appeals court decision was to uphold a position taken last week by the Carter administration in legal briefs submitted to the court. The government contended then that the bistate transportation agency's ban had been "unfair, dilatory, arbitrary and unreasonable," but it asserted nontheless that federal supremacy in such disputes was not a valid argument.

Kaufman warned that a "serious question" had been raised about the effects of the dispute on American foreign treaty agreements. He said, "The delicate framework of international understanding that makes possible the flourishing of transoceanic air travel has already been rent by the Concorde controversy."

The appellate court urged the Port Authority - whatever the outcome of Pollack's hearing - to finish its study of the impact of the SST and "fix reasonable noise standards with dispatch." Kaufman said the court feels "it is in the interest of all concerned that this interminable strife be brought to an end."

However with the case now going back to district court, the chances of SST tests beginning here soon seemed remote. Regardless of the results of the new hearings, a new appeal is considered certain and the case probably will go to the Supreme Court, court sources suggested.