Last weekend's news hit the International Olympic Committee with a jolt: The U.N. Security Council was imposing sanctions on Serbian-controlled Yugoslavia, including barring the nation from participation in next month's Summer Olympics in Barcelona.

While the IOC is not bound by the U.N. resolution, the very thought of political interference dashed the shining hope that the 1992 Summer Games, July 25 to Aug. 9, would be the first without boycott or no-shows since the tragic 1972 Munich Games. IOC officials are expecting the largest and greatest Olympics the world has seen: South Africa and Cuba are back, Germany is united, 12 former Soviet republics are unified for one last time and the United States is stronger than ever.

But the thought of losing about 135 Yugoslav athletes to political problems has turned joy to sadness at IOC headquarters in Lausanne, Switzerland.

"I don't want innocent athletes to pay the price," Francois Carrard, IOC director general, said during an interview in Washington Monday. "We were very excited to have a totally boycott-free Games, with everyone there, but, unfortunately, we are used to the problem. To us, it's a constant concern. We only breathe easily when the closing ceremonies come to an end."

The Yugoslav athletes, including the water polo team that won the gold medal in 1984 and 1988, are not yet officially out of the Games. President Juan Antonio Samaranch said yesterday he will meet with the Yugoslav Olympic Committee in the next week and will announce a decision by June 15, according to Carrard.

"We don't want to rush too much," Carrard said yesterday. "We want to see what develops in the next few days before we make our decision."

If the IOC lived in a vacuum, it would invite the Yugoslavs.

"As a matter of principle, the IOC does not like a ban on sports for political reasons," Carrard said. "We don't like this form of sanction and never favor it. What we will do is still open at this stage. You know, sometimes the last channels of communication can be sports. During the dispute between the two Koreas, for instance, sports was the only way they would communicate. At one point, the two countries were speaking only in IOC meetings. Because of this, we always ask, 'Do we have to punish the athletes?' It's always the innocent athletes who pay the price."

If the IOC goes through with its own ban, the Barcelona Games would lose the Yugoslav women's basketball team, which qualified for the Olympics by virtue of a second-place finish at the 1990 world championships. The International Basketball Federation currently is holding a tournament to select four teams for the eight-team field (the United States, Cuba and Spain already have qualified for the Games) and has added a game to the qualifying tournament to determine the fifth-place team in case Yugoslavia is forced to withdraw.

The Yugoslav men's basketball team, which had not yet qualified for the Olympics, stopped practicing for the European qualification tournament later this month in France and was going home, the Associated Press reported. The Yugoslavs, led by Los Angeles Laker Vlade Divac, were one of the favorites to win one of the four Olympic spots in the field of 26, although Lithuania, Croatia, the Unified Team of Former Soviet Republics, Germany and Italy are believed to be stronger teams.

"It's simply not fair," Divac, of Serbia, told AP. "We are not politicians and warriors. We are only sportsmen and sports should not mix with politics."

Otherwise, confusion reigns about who is playing for whom within the old Yugoslavia, and not even the IOC is able to figure it out.

"The water polo team, the men's and women's team handball teams. . . . " Gilbert Felli, IOC sports director, said yesterday. "They have qualified for the Olympics. We know there are some track and field athletes, but we don't have their names because we don't know their nationalities. With some athletes competing for Croatia and others for Slovenia, it's very difficult to tell what's left."

Even if the IOC decides to keep open its invitation to Yugoslavia, there is no guarantee the Spanish government will honor Yugoslav passports at its border. Sources close to the situation said Spain expressed reservations about the inclusion of sports in the U.N. sanctions to avoid political battles at its Olympics. But now that the resolution is in place, Spain could honor it by refusing entry to Yugoslavs.

The prospective Yugoslav ban has thrown a wet blanket over the grand plans of the Barcelona Games' organizers, at least for the moment. It seems that everything in sports becomes bigger and better as the years move on, and the Olympics are no exception. A record 173 nations (172 without Yugoslavia) are expected; there were 160 in Seoul in 1988, the previous high. There is space for 10,000 athletes, although as many as 11,000 could come. (The IOC is calling every nation's Olympic committee, Felli said, asking it to cut back where it can.) There were 9,627 athletes in Seoul, which was an Olympic record.

Part of the reason for the increase is the addition of new nations such as Estonia, Latvia and Lithuania and the return to the fold of such nations as Cuba and South Africa. The Cubans are coming back after joining the Soviet-led boycott of the 1984 Los Angeles Games and a boycott in support of North Korea at the 1988 Seoul Olympics. They are very strong in baseball and boxing and could do well in volleyball and a few track and field events. Cuban President Fidel Castro has told the IOC he is coming to Barcelona to watch his athletes.

South Africa is expected to send between 90 and 100 athletes to the Olympics in 18 individual sports, Felli said. The nation, barred from the Games since 1960 because of its racial policies, will not field any teams in Barcelona because it rejoined the Olympic movement too late to qualify. South Africans will participate in track and field, swimming, rowing, yachting and tennis, among others.

There has been some difficulty in selecting a South African team that is both strong athletically and balanced racially, Carrard said. Many of the top athletes in the country are white because of the way the system worked in the past.

"We want a racially representative team; everybody wants that," he said. "The difficulty comes in how to create that without discriminating against one group or another. The idea behind the return to the Olympics is to help South Africa, not hurt it."

The top three medal-winning nations almost certainly will be the United States, Germany and the Unified Team, not necessarily in that order. While the U.S. Olympic team now is thriving on unprecedented corporate support, Germany grapples with meshing two opposing systems and the former Soviet Union tries to hang together for one more Games, minus the three Baltic republics.

When an individual athlete from the Unified Team wins a gold medal this summer, the anthem and flag of the athlete's republic will be used. This is a departure from the practice at the Winter Olympics in Albertville, when the Olympic hymn and flag were used for all Unified Team gold medals.

For team sports, if the Unified Team wins the gold, the Olympic hymn and flag will be used unless every athlete is from the same republic. In that case that republic's anthem will be played and flag will be raised. All medals will be added to the Unified Team's total.

The 12 republics will parade into the opening ceremonies as one delegation, but athletes may wear a patch on their uniforms and carry small flags identifying their republic.

Come Jan. 1, 1993, however, the 12 republics either will be on their own athletically or will form sports alliances with another republic -- and the Unified Team will be no more.