John Kerr sat comfortably on the grass yesterday at RFK Stadium's auxiliary field, putting on his club team's game socks and reflecting on the U.S. national soccer team's 1-0 loss to Costa Rica Friday night in the World Cup qualifying round at Torrance, Calif.

"It was the best game we played in the series," said Kerr, a graduate of Falls Church High School who recently completed his sophomore year at Duke. "They had one or two opportunities and they capitalized. We had the opportunities and didn't capitalize. When you miss the opportunities, you lose faith.

"We were very optimistic because the (U.S. Soccer) Federation was going to give us more time to prepare for the next round," he said. "Most of our players would have been able to go from indoor (MISL season) to outdoor because of the extra time."

The U.S. team tied Costa Rica, 1-1, on a goal by Kerr late in the first half of the first elimination game and needed only a tie in Friday's game to advance to the final qualifying round this summer.

Instead, Costa Rica advanced to the next round of qualifying for the 1986 Cup and the United States was eliminated.

Costa Rica converted the only shot it needed, scoring off a free kick at 34:50 in the first half. After the ball was deflected from a group of players in front of the goal, Evaristo Coronado kicked the ball into a wide-open net.

Yesterday, Kerr was at the auxiliary field at RFK Stadium as his club team, Spartan of Fairfax, played Espana of Washington in the Metropolitan D.C./Virginia State Cup. Espana won, 2-1, as Kerr scored Spartan's only goal.

Both teams will compete in the national semifinals as East Region representatives June 29 in St. Louis. Spartan will play for the National Open Cup, which includes professionals. Espana will play for the National Cup, which is closed to amateurs.

In the first half yesterday, Kerr showed the skills that earned him a spot on the national team. After receiving a pass, he spun around while dribbling and left defender Ronnald Simmons on his back side. At 70:00, he scored on a rebound off a shot that deflected off the left goal post for a 1-0 lead.

Howard University's Phillip Gyau tied the match, and Fernando Iturbe scored the winner with seven minutes left.