It started as one of those sweepingly decent gestures to give foreign residents of the United States one of the last rights they don't have - the right to own an airplane.

But by the time Congress completed its humanitarian act last month, it set off alarm bells in the financial community, stunned the airlines and reddened faces on Capitol Hill.

For what they had passed, and what President Carter signed into law Nov. 9, was making it impossible for U.S. corporations to register their planes here if they fly them primarily in another country.

That means that such carriers as World Airways a major charter firm, and Pan American and Eastern Airlines would lose their vital U.S. registration for planes they use overseas.

For World Airways, that would be whole ball game - its fleet of more than 20 planes is flown only abroad. For Pan Am, it would mean 13 jets based in Germany. For Eastern, at least 10 jets under lease in Japan.

Beyond that, many U.S. businesses which register their corporate aircraft here, but use them only in distant corners of the globe, would face the same problem.

Congressional leaders have promised quick action to correct the linguistic mischief. Word has come from the Federal Aviation Administration that it knows Congress meant something else, so it will go slow on enforcement of the new statute.

"Legally, the FAA has no choice - it has to enforce the law," said Stanley J. Green vice president of the General Aviation Manufacturers Association. "What do we do in the meantime? Not fly? Not sell airplanes?"

Added Green: "It can put a question mark on a helluva lot of airplanes, because weird legal issues would arise. It could hurt sales. Banks don't want to make loans on sales unless they can control through registry."

The problem evolves from passage of a package of amendments to the Federal Aviation Act, which President Carter signed into law.

One of the amendments was intended to allow alien residents of the United States, who can do virtually everything else but vote, finally to own airplanes.

That goal was sought years ago by the Aircraft Owners and Pilots Association, which has more than 200,0000 members. Such ran amendment was approved by the House and Senate last year, but it did not become law.

This year, AOPA renewed its fight with another ally, the general aviation manufacturers, who want to sell as many planes as they can. GAMA wanted the law to further specify that foreign-controlled corporations also could own and register planes here.

Congress had no problem with that, but then the tinkering began and language said that a U.S. corporation could register its planes here only if the aircraft are "based in and primarily used in the United States."

The proverbial spaghetti thereupon hit the fan.

Banks went into a dither, U.S. registry is one way they maintain a grip on the collateral - that is, the planes - for which they make purchase loans.

Airlines went into a tailspin. The U.S. registry provides certain assurances of a plane's airworthiness and it gives some advantages in lease and sale arrangements.

Very quickly, they got their message of anguish to Capitol Hill. Before Congress adjourned last week until Jan. 19, Rep. Glenn M. Anderson (D-Calif), introduced a bill to rectify the situation.

Congress has enough problems without parading its mistakes before the world, so Anderson kept his explanation low-key.

"Since enactment," he told the House. "it has been found that the amendment has a drafting ambiguity which raises substantial legal problems.

Because of this "inadvertence", Anderson said, many, U.S. international air carriers technically would be in violation since their planes are used mostly abroad.

Congressional assurances notwithstanding, all is not calm in the atmosphere of the overseas-based American air carrier.

"It's raising havoc and I'm sure it will be changed," said Charles Spence of AOPA. "Our concern is that in the mills of Congress the cogs grind awfully show. If it can't be corrected it could be serious."

Jack Reiter, a vice president of World Airways, wants to see the amendment to the amendment approved before he will declare an end to worry.

"Realistically," Reiter said, "it will wait until Congress comes back next month . . . but if an attorney is involved in buying or leasing a plane from a U.S. company, legal questions could come up . . ."

Jack Teiter's voice sort of tailed off, no unlike a jet trail vanishing over the horizon.