Let the '84 games begin!

Part sport, part spectacle, the 1984 Los Angeles Olympics opening this weekend promises to be a world-class show. By the time it ends with the snuffing out of the Olympic torch on Aug. 12, more than 2 billion people will have watched the games in person and on television.

Despite the Soviet-bloc pullout, a record 140 countries are participating - sending some 7,800 competitors, 597 of whom are from the United States. China is sending a delegation for the first time since 1932, and Romania, alone among the East-bloc nations, plans to be here.

Some 8,000 journalists from 150 nations will be covering the events.

The two specially built main Olympic villages, on the campuses of the University of California at Los Angeles and the University of Southern California, resemble small cities; they are designed to house 12,000 people from around the world.

Even without the athletically powerful Soviets and East Germans, the competition in 23 sports beginning Sunday will focus attention on many of the world's foremost sportsmen and sportswomen. Among them are defending decathlon champion Daley Thompson of Great Britain and versatile sprinter-jumper Carl Lewis of the United States, who is attempting to win the same four gold medals won by Jesse Owens in Berlin in 1936.

This year's site is also rich with tradition. The Los Angeles Memorial Coliseum, where the Olympic torch ended its cross-country trip this week and where the opening ceremony will be held Saturday, was the site of the track-and-field portion of the 1932 Los Angeles summer games. Here hurtler Mildred (Babe) Didrikson ran and jumped her way into the history books. Here the first photo-finish camera gave track-and-field judges an entirely new sense of confidence.

That was during the Great Depression, with millions of people out of work across the country. But ticket prices were held to between 50 cents and $3, and the '32 games turned a profit of slightly more than $1 million - which was later given to taxpayers.

This year's Olympics, which charged 30 corporate sponsors a minimum of $4 million each and garnered $225 million by selling TV rights, is also expected to finish in the black - although the profit margin will be considerably less than originally expected.

More than $120 million has reportedly been paid for security. Aware of recent threats, and wanting to avoid any repetition of the tragedy at Munich in 1972, when terrorists killed a number of Israeli athletes and trainers, the Los Angeles Olympic Organizing Committee (LAOOC) has invested in bomb detection gear , sophisticated robots, and a fleet of helicopters to patrol during the games almost without interruption.

Security, in fact, has been a subject central to the politics that, as usual, surround the games. The official Soviet reason for boycotting the games is that there are too many holes in the security system.

That, however, has not detered Romania's Nadia Comaneci, who is here as the guest of the LAOOC. Miss Comaneci, who as a 14-year-old astounded the world at the 1976 Montreal games by earning the first perfect gymnastic scores in Olympic history, has come out of retirement to help train Romanian athletes while she is here and act as a gymnastics consultant to the LAOOC.

The organizers have also made sure that for the first time in history, a President of the United States will open an Olympic Games - an honor Ronald Reagan agreed to perform back in 1982. Theodore Roosevelt was not there when St. Louis was host to the games in 1904, although he did send his daughter, Alice, to serve in his place.

When Franklin Delano Roosevelt opened the 1932 Winter Games at Lake Placid, N.Y., he had not yet been elected to the presidency. The '32 summer Olympics featured Vice-President Charles Curtis, who came instead of President Herbert Hoover. Vice-President Richard M. Nixon opened the 1960 Winter Games at Squaw Valley, Calif., while the 1980 Winter Olympics (again at Lake Placid) were officially launched by then Vice-President Walter F. Mondale.

The US Olympic Committee has spent more than $250,000 since January on its new and thorough drug-control program, aimed at countering the use of drugs by US athletes. ''There is no doubt that this program, which has been a war on drugs and not on our athletes, has been effective in reducing dependence on performance-enhancing drugs,'' explains US Olympic Committee executive director F. Don Miller.