Providential II, a colt whose very presence in the $250,000 Washington, D.C. International seemed hard to explain, upset some of the best turf horses of Europe and America at Laurel Race Course yesterday.

He hadn't won a stakes race in 1981. He had won a total of two races in the past two years. Providential II seemed merely to have come along for the ride with his more illustrious stablemate, the favorite Galaxy Libra. But at the end, he had scored a one-length victory over the good French filly, April Run, with Galaxy Libra a soundly beaten third.

Although he was technically an American representative and gave this country its 15th victory in 30 runnings of this race, Providential II had a true international background. He was bred in Ireland by an American, Bert Firestone; sold for more than $1 million to Serge Fradkoff, a Swiss gem dealer; raced in France and Argentina, and was finally sent to trainer Charles Whittingham in the United States. Yesterday, he was ridden by a French jockey, Alain Lequeux, because Panamanian Laffit Pincay was unavailable.

The $120,000 first-place money increased Providential II's career earnings to $371,579.

All week long, as Whittingham was questioned about the chances of Galaxy Libra, he kept saying, "My other horse might surprise everybody." Nobody listened. But while Laurel President John D. Schapiro might have issued Providential II his invitation on the basis of his eclectic background, Whittingham sensed that the 4-year-old was just beginning to approach his peak form. At about the midway point of the International, the 19,804 spectators at Laurel, the smallest crowd in International history, were beginning to see that he was right.

The early stages of the race had developed very predictably. None of the 10 entrants was a front-runner by nature, and none of the jockeys wanted the early lead. While Match the Hatch and Siapa Rajah III reluctantly set the pace, April Run stalked them and Providential II sat within striking distance in sixth place.

As the field covered the three-quarters of a mile in a dawdling 1:15 3/5, none of the jockeys tried to make a decisive early move. Everyone was waiting until the final turn. Trouble was awaiting many of them.

Beldale Flutter accelerated strongly on the rail into a wall of horses, forcing jockey Pat Eddery to put on the brakes. Open Call hugged the rail on the turn, but jockey Jorge Velasquez couldn't find an inch of running room.

April Run moved three-wide around the pacesetters, with Providential II following her footsteps. Galaxy Libra made the strongest move of all on the turn, but was running wide and was forced to lose ground.

Amidst all this congestion, Lequeux saw some daylight. "At the end of the turn," he said, "there was an opening on the rail." He angled his mount there, inside April Run, and he would say later, "I knew I had the race won."

Just as Providential II drew abreast of April Run, the latter's jockey, Philippe Paquet, dropped his whip. This was a much less egregious bit of ineptitude than he displayed here in 1979, when he was singlehandedly responsible for the defeat of the favored Le Marmot, but it certainly didn't help April Run. Providential II slowly pulled away from her through the stretch, running the last quarter-mile in 24 seconds flat, covering the 1 1/2 miles in 2:31 1/5.

If Providential II had not been coupled in the wagering with Galaxy Libra, he would have been an extreme longshot. In New York's Off-Track Betting, where he was a separate betting unit, he paid $66.40 to win. His backers at Laurel had to settle for $6.40, $3.40 and $3.40 across the board. April Run returned $4 and $3.60.

The outcome of the race had to be bittersweet for Bert Firestone, the owner of April Run, who bred Providential II. Firestone looked like the winner in that transaction when the colt managed to win only one stakes races as a 3-year-old. After that unsensational campaign, Fradkoff sent him to Whittingham, the brilliant West Coast trainer who has won more stakes races than any member of his profession.

"Charlie is known to be very patient with horses," Fradkoff said, "and I am known to be very patient with trainers." Whittingham gave the colt several months rest, and raced him only five times in the summer and fall. He managed to win one nondescript allowance race and finished second in a minor stake. Until this afternoon, that seemed to be a highly unlikely set of credentials for an International winner.