The U.S. Navy was willing to lend Britain an aircraft carrier during its 1982 campaign to retake the Falkland Islands from Argentina if the Royal Navy lost either of its two carriers, Defense Department officials said yesterday.

Although an offer to use the USS Guam, a helicopter carrier, was not made because the need did not arise, officials said such discussions took place as part of a large-scale effort to try to ensure that Britain's 100-ship armada did not meet defeat in a battle 8,000 miles from its home waters.

Pentagon officials were asked about the U.S. role in the Falklands campaign--which began with the Argentine seizure of the islands on April 2 and ended June 14 after the British recaptured them--in the aftermath of a detailed report on the extent of U.S. help that appears this week in the respected British magazine The Economist.

The magazine said the Falklands campaign "could not have been mounted, let alone won, without American help."

Pentagon officials confirmed many of the details in the report, including the fact that the United States repositioned a spy satellite, using up scarce fuel and thus shortening the satellite's life in space, from its Soviet-watching orbit in the Northern Hemisphere to a place over the South Atlantic where it could provide intelligence to the British fleet.

The officials said American intelligence information, provided by means other than just satellites, probably made the key difference between winning and losing because the Argentine attacks on the Royal Navy would have been even more effective if the British had not had the information.

Pentagon officials spoke of extraordinary coordination between the American and British services. The United States supplied 12.5 million gallons of aviation fuel diverted from U.S. stockpiles, along with hundreds of Sidewinder missiles, airfield matting, thousands of rounds of mortar shells and other equipment, they said.

Defense Secretary Caspar W. Weinberger played a "bold" and "daring" role, some Pentagon officials said. Both he and the U.S. Navy high command feared that Britain could be sailing into a disaster and that a military defeat at the hands of Argentina would be a severe setback to the deterrent quality of the entire North Atlantic alliance, they said.

The magazine reports that Weinberger got the approval of President Reagan for his efforts. But it suggests that those efforts were not aired before the full White House National Security Council and that former secretary of state Alexander M. Haig Jr., who was seeking to negotiate a settlement between Britain and Argentina for the first month of the crisis, also may have not been fully informed about the extent of U.S. help to the British.

Pentagon officials said Weinberger's efforts on behalf of Britain were reported at the Cabinet level, but once that was done he moved quickly, and they said they were not certain how much was known and by whom about specific actions.