There is a joke among American and other basketball players who compete internationally that goes: "Pressure is being on the free-throw line in the Soviet Union in the '80 Olympics, with the game on the line and some guy reaching for your visa."

Nobody was seen scrambling for center Dino Meneghin's visa, but every other imaginable pressure was evident as he stepped to the foul line with 12 seconds left in a semifinal game tonight and the Italians ahead of the Soviets by two points.

With whistles and jeers echoing off each other in the immense basketball arena, Meneghin sank both shots and assured Italy of an upset that ended at 87-85 when the Soviets sank a harmless final-second basket.

The favored Soviets still have a chance to win the gold. But now so do Italy, Yugoslavia, Spain and Brazil. Italy nearly blew an eight-point lead in the final minutes. Renato Villaota led the Italians with 21 points. lSergei Belov had 21 for the Soviets.

"For me, tonight's win is the same as a medal," Italian Coach Alessandro Gamba said. "Nobody can even remember when the Soviet team was beaten at home before. But we're not drinking champagne yet. We'll wait until the finals for that."

The East German women were mining more gold in the Olympic swim center again tonight. Petra Schneider set a world record of 4:36.29 in the 400-meter individual medley as the Germans won their ninth gold in 10 events.

Ute Geweniger won the gold in the 100-meter breastroke in 1:10.22 and Heike Dahne set an Olympic record of 8:36.09 in qualifying for Sunday's 800-meter freestyle final. Martina Jaschke won the women's platform diving with 596.250 points.

Sara Simeoni of Italy, reluctant to come to the Games because she wanted her country to join the United States-led boycott, won the women's high jump with an Olympic record 6 feet 5 1/2 inches. She holds the world record of 6-7.

Soviet Yurik Vardanyan set three world weightlifting records and won the gold medal in the 182-pound class. His records were for lifing 390.5 pounds in the snatch, 499.5 pounds in the jerk, and a total of 890 pounds.

One Puerto Rican boxer, Alberto Mercado, lost because of a cut tonight, and another, Jose Molina, advanced to the quarterfinals for the same reason.

"I felt very sad," Molina said following his 139-pound bout, stopped after East German Dietmar Schwartz suffered a bad cut on his nose, "because my pal who had a good opportunity for a gold medal lost that opportunity after all of his sacrifices."

Said German Rieckenhoff, president of the Puerto Rican Olympic Committee: "If Mercado wouldn't have taken a strong position on the boycott, Puerto Rico wouldn't have been here."

Yelena Davydova, the 18-year-old Soviet who edged Romanian Nadia Comaneci for the all-around gold medal in women's gymastics, was such an outsider that she was not even introduced by the Soviets as a contender when the competition began. In an elaborate press conference, the Soviets introduced their heavy hitters and she was left out.