THE Pan American Games, which begin today in Havana, are the first major international sporting event to take place in Fidel Castro's Cuba. The United States is sending some 700 athletes to the games, along with coaches and trainers, sports officials, and journalists.The usual fraternization that accompanies international competition will expose a lot of Americans and Cubans to each other's culture for the first time. More important, television coverage of the games will give the US people an unprecedented window on a land that, though only 90 miles from Florida, for 30 years has been shrouded by geopolitics. Except for a trickle of invited guests like journalists and scholars, few Americans have seen Cuba in those 30 years, owing to US legal restraints. For the same reason, there won't be many American spectators in the stands during the two weeks of the Pan Am Games. So TV will take on added significance not just as a conduit for athletic thrills, but as a conduit to Americans of a hidden land and its people. One shouldn't overstate the games' political significance. US and Cuban athletes have competed often in international forums, so that aspect isn't new. And despite the common bromides, sport has limited power to breach political barriers; it wasn't East German swimmers who brought down the Berlin Wall. US differences with Cuba - the new Albania of communist hard-liners - are deep, and won't be bridged by sprinters and gymnasts. But even if Cuban sponsorship of the games has little diplomatic fallout, we welcome the event for a chance to see and "experience" the island. As was said of Iraq during the war, the US quarrel is with Cuba's leader, not its people. It's sad that a people with historical ties to the United States, and whose emigrants have contributed a salsa tang to the American cultural mix, should be so cut off from American empathy. If only as a people-to-people contact, the TV images beamed from Havana will be as refreshing as a tropical breeze.