The New York Port Authority's refusal to permit trial flights of the Concorde into John F. Kennedy International Airport "may be so unreasonable" as to constitute legal grounds for a court to require the flights, the Carter administration said yesterday.

In a brief filed in the second U.S. Court of Appeals in New York City, the Administration called the Port Authority's ban on Concorde tests "unfortunate and ill-advised" and said its refusal to permit a "fair test" has cost the United States "the good will of our allies." The Concorde is a joint venture of the British and the French.

Nontheless, the Government brief said, the Port Authority and other airport operators are well within their rights when they impose specific noise regulations on aircraft using their facilities. That rule does not change just because the federal government authorized Concorde flights to the United States, the government argued.

That complicated legal reasoning is the first official statement in court of the federal position on the Concorde New York controversy. The government was brought into the case when the Court of Appeals ordered both the State and Transporatation departments to answer specific questions on the matter. The views of the two departments were reconciled in a series of meetings at the White House last week and officially filed by the Justice Department yesterday.

Essentially, the U.S. brief expresses the same position the government has held, through two administrations - that landing rights for the Concorde may be decided locally and that localities may enforce noise rules.

At the same time, the brief expresses strong support for the British and the French, who have insisted that they need the New York market to prove whether their sleek aircraft can operate profitably.

The appellate court is reviewing a decision by a federal district judge that orders the Port Authority to permit test flights of the supersonic transport plane. The Port Authority has never issued an irrevocable ban against the Concorde, and in fact has delayed taking any final position for more than a year. Former Transportation Secretary William T. Coleman Jr. authorized 16 months of Concorde test flights to Washington and New York in February, 1976.

The tests, to be conducted as regularly scheduled passenger service, would determine the impact on people and the environment of Concorde's noise and exhoust emissions. A final decision would then be made on whether Concorde could continue service to the United States.

Concorde has been flying for 12 months to Dulles, but has never touched down at Kennedy, as the Port Authority has debated and studied the issue.

Air France and British Airways, the only two airlines currently operating the plane, which flies at twice the speed of sound, finally went into the U.S. courts to seek New York landing rights.

A central, underlying issue a U.S. law that makes airport operators - not airlines or the federal government - liable for damages in aviation noise suits. The U.S. government has tried vigorously to protect its immunity from such suits throughout the Concorde debate.

The administration declined to answer one of the appellate courts questions - whether the Concorde ban violated any treaties. To answer, the government said, might impede current negotiations between the United States and Great Britain on a new treaty to guarantee mutual aviation landing rights. The current agreements expires June 22.