Pass the petitions to get President Carter to pardon Finbar B. Kenny. The unlucky Finbar is the first, and let us hope the last and only, American to be convicted of criminally violating the foreign Corrupt Practices Act.

The crime for which this felonious Finbar person has pled guilty and will have to pay a $50,000 fine is truly one which should be set to music. It doesn't belong in the criminal courts, but on the stage as part of a romantic comedy.

The site of the crime is a quasi-national entity called the Cook Islands. There are eight of these islands, situated 1,800 miles northeast of New Zealand, which is only 200 miles southwest of nowhere at all. Eighteen thousand souls proudly call themselves citizens of the Cook Islands, and presumably sing its national anthem, salute its flag and defend its fair hills and sweet glades from foreign attack.

The nation's primary export is postage stamps; a million and a half dollars, or 20 percent of Cook Islands' revenue, is derived from these stamps. The exclusive, worldwide marketing franchise for the highly prized stamps is held by a company called the Cook Island Development Corporation, headed by the nefarious Finbar.

The accusation which has brought the gentleman to a guilty plea in a federal court is that the aforesaid Finbar made available $337,000 to one Sir Albert Henry to help secure the good knight's reelection as prime minister of the Cook Islands. The money is supposed to have been used to ferry Cook Island citizens back from New Zealand to vote.

Sir Albert is in the soup too. The knight has been deposed from his prime ministership and all manner of awful things are being inflicted on him.

Some American officials estimate that this silly law, passed at the end of 1977, is currently costing in the vicinity of a billion dollars a year in sales and contracts lost. Whatever the figure, we are the only nation in the world that makes commercial activities by our own nationals a crime when committed on another nation's soil. Though, for example, it may not be against that country's law to bribe his excellency, the minister of trade of Dudd, an American who does it can apparently be jailed by a federal court in New York because the act is illegal here.

It is a difficult-enough job for any government to enforce its own laws on its own sovereign territory, without having to enforce somebody else's. Look at the difficulty we're having making Chile cough up the Chilean nationals our Justice Department believes are responsible for the murder of Orlando Letelier, the Chilean exile who was blown up on a Washington street.

Any nation which doesn't like the way Americans inside its borders are behaving has a number of ways of taking care of the problem. They can toss the Americans out, or try them in their own law courts; or, if the Americans have left the country, they can sign an extradition treaty with us, so that the American accused of committing crimes can be sent to face the music.

We saw how helpful the South Koreans have been in punishing their citizens for bribing our public officials for grain contracts. The did everything they could to sabotage, block, delay and stymie the investigation. South Korean nationals, whose testimony might have cracked open the case, were hidden over there by their government so that almost everyone suspected of breaking our laws -- South Koreans and American congressmen -- got away with it. Yet part of this ill-starred Finbar Kenny's punishment is to go all the way to the Cook Islands at his own expense to help the prosecution's case down there.

Be it noted that our fellow members of the United Nations have declined our invitation to pass a similar corrupt-practices law themselves. They're content to let us derive whatever peculiar satisfaction we get out of playing the idiot while they steal the business from us. You would have thought that, at this moment, when we're concerned about an adverse balance of trade and too few exports, the Justice Department might have forgotten about this law. There must be more dangerous characters to prosecute than American salesmen out with their order books.

Even to have such a law is a continuing act of perverse moral snobbery. It is as though we were telling the rest of the world that we're so law-abiding ourselves, so punctilious about obeying all our own rules, we want to help others become as good as we are.

So write President Carter to pardon Finbar. You might try sending the letter with a Cook Islands stamp on it.