Somewhere in the world, there’s a navy blue suitcase with a small pack of explosives tucked in its side pocket.

Four days after police at Charles de Gaulle Airport slipped some plastic explosives into a random passenger’s bag as part of an exercise for sniffer dogs, it is still missing — and authorities are stumped and embarrassed.

Police have sought to minimize public concern by insisting there’s nothing to worry about: The explosives had no detonator and are unlikely to pose a danger.

But that does little to diminish the fact that the French airport security has been planting explosives in the suitcases of unsuspecting passengers — all in the name of safety.

“That’s pretty scary,” said Chadi Kawkabani, an American tourist wheeling his suitcase along the Champs-Elysees on Tuesday before heading to the airport.

“I picture myself opening my bag at home,” said Kawkabani, a marketing director from Boston. “You might think terrorists planted the explosive — and they could come to your house to get it back!”

“Imagine getting caught at your arrival,” said Laurence Grassiet, a 32-year-old Parisian hair stylist. “You’d be in for a hard time!”

Any one of 100 flights

Authorities believe the suitcase left Paris between 5 p.m. and 7 p.m. on Friday and could have wound up on any of about 100 flights.

“There were flights that went to the United States, to Japan, South America,” said police spokesman Pierre Bouquin. “Basically, it could have gone anywhere — to the four corners of the world.”

Authorities at airports in New York and Los Angeles launched a fruitless search for the suitcase after French aviation officials issued a global alert to be on the lookout for the bag.

The training exercise was aimed at providing sniffer dogs a real-life airport scenario — a technique that has been used for years, said Bouquin.

Blame, in this case, cannot be placed on the dogs.

Two police officers involved in the exercise stashed a cell-phone sized pack of plastic explosives into the side pocket of the navy blue suitcase as it rolled along a conveyer belt.

One dog successfully identified the bag, but police then lost track of it when they went to fetch a second dog for the exercise.

“That’s how the explosives disappeared,” said Bouquin, noting that police have not lost hope of retrieving the explosives — someday.

“Sometimes, side pockets don’t get unpacked immediately. Maybe the person who has this product will find it in the future.”

Clouseau on the case?

For France’s high-minded Le Monde newspaper, the mishap rings of Inspector Clouseau, the bungling, fictional French detective of “Pink Panther” fame.

“Inspector Clouseau works the weekend at (Charles de Gaulle),” was the headline of a story in Le Monde’s Tuesday edition.

“The cause of this planetary search is both strange and comical,” the newspaper said. “We warmly congratulate the sniffer dog brigade ... for this remarkable exploit: having succeeded in placing an explosive on a departing plane.”

Police quickly ordered a halt to the practice, assuring that dogs would stop using real luggage for practice. Interior Minister Dominique de Villepin said the incident was “totally reprehensible and scandalous” and vowed that punishment would be doled out accordingly.

The officers behind the mix-up have been subject to a “disciplinary procedure,” said Bouquin, declining to elaborate.

Paris’ airport authority, meanwhile, has sought to distance itself from the mishap.

“It’s true that it’s astonishing,” said Corinne Bokobza, spokeswoman for Aeroports de Paris. “But we don’t know about all the practices carried out by the police.”

As for lost bags, they tend to turn up “pretty quickly,” she said, generally within a week.

But that’s when the bag is ticketed and traceable through the computer system. Finding a navy blue suitcase lost somewhere in the wide world, she said, “could take a while.”