The politically-scarred Moscow Olympics officially begin here Saturday with opening ceremonies that are certain to be grandiose, spectacular in their pageantry but hollow and joyless -- inevitably haunted by the Soviet military presence in neighboring Afghanistan that has prompted the United States and approximately 50 other nations to stay away.

Soviet President Leonid Brezhnev will declare the Games of the 22nd Olympiad open amid a dazzling extravaganza of color and sound at 103,000-seat Lenin Central Stadium. But much of the world will view this summer's lighting of the Olympic Flame as nothing but a propaganda charade.

Beneath the festive facade created by 16,000 singers and dancers and gymnasts in full parade regalia will be an underlying mood of sadness, suspicion, cynicism and gloom.

The absence of athletes from the United States, West Germany, Japan, China, Canada and other countries assures that the Games themselves will lack their usual sparkle and competitive preeminence. Among 203 events in 21 sports over the next fortnight, there are bound to be many tarnished medals presented.

The first Olympics in a Communist country always were destined to be a highly politicized occasion, a clash of ideologies on a global scale as well as of athletes on a deeply personal level.

But the Soviet invasion of Afghanistan last December made a Cold War battlefield of a festival that, according to the battered Olympic ideal, is supposed to celebrate peace and understanding through sport. The Moscow Games are truly Olympian only as a political event.

"This is a wedding at which the bride appears in a dress of paper, not of lace," said an official of the Italian Olympic Committee, which, like many of the other Western European nations that did not join the U.S.-led boycott, sent a team reduced in number and quality because of political pressures at home.

"The Soviets wanted these to be colossal Games," he said. "They wanted to show the world that they could stage the Olympics in a very grand manner. But with 50 nations and so many of the best athletes missing, there is no way you can call these colossal Games."

Of the 146 countries that have recognized national Olympic committees and therefore were eligible to enter, 81 have sent athletes to Moscow. A total of 5,687 athletes and 1,985 team officials have been registered at the Olympic Village, a sprawling and heavily guarded complex in the southern reaches of the Soviet capital.

The Soviet organizers originally expected about 120 countries and 10,000 athletes to take part. They are disappointed. However, the roster of participating countries and competitors is far larger than the Carter administration envisioned when it called for a massive boycott in February.

Much of Western Europe is represented at the Games. However, many allies have sent teams that are well below maximum strength because individual athletes or sports federations within their national Olympic committees decided not to come.

New Zealand, for instance, entered only four athletes in a delegation originally expected to include about 100. Puerto Rico, which has its own Olympic committee even though it is a U.S. commonwealth, has just three boxers here.

Great Britain's equestrian, yachting, shooting and field hockey teams heeded Prime Minister Margaret Thatcher's persistent appeals to stay home. Individual athletes from other British sports federations, including the captain of the fencing team, bypassed Moscow as a matter of conscience, or because of political pressures.

In numerous instances, athletes were given no choice. The governments of Italy and some other countries ordered armed services personnel not to go to Moscow. In Italy's case, this ban affected 80 athletes, including strong medal contenders in track and field, modern pentathlon, swimming, fencing, shooting and equestrian event.

The Communist-bloc nations, including such athletic powerhouses as the Soviet Union, East Germany, and Cuba, are of course, in Moscow at full strength.Some sports that are traditionally dominated by these countries -- such as weightlifting, team handball and canoeing -- will be virtually unaffected by the boycott.

Others, such as women's field hockey, have been decimated to a ludicrous degree. A month ago, the Soviet women were the only entry. The tournament has been filled with puppet teams far below usual Olympic standard. It is a sham.

Surely, there will be memorable moments of grace and glory -- athletic feats to remind us that the Olympics are at heart a sporting event, capable of producing transcedant artistry. There will be human drama.

The duels between Britain's supreme middle-distance runners, Sebastian Coe and Steve Ovette, in the 800 and 1,500 meters, would be dream races in any Olympics. Between them, they hold four world records, and the rivalry is enhanced because they are countrymen of contrasting personality and temperament who don't care for each other, and have spent years avoiding head-to-head meetings.

The anticipated heavyweight boxing bout between two-time gold medalist Teofilo Stevenson of Cuba and Sweden's Anders Eklund, who is coached by former world champion Floyd Patterson, could be one of the most interesting confrontations in an Olympic ring since 1972.

The battle for supremacy in women's gymnastics between Romania and the Soviet Union -- perennial world team champion until the Romanians, even without injured star Nadia Comaneci, took the title away in Fort Worth last December -- is no less fascinating because of the boycott.

Magnificent performers of Games past will be back, trying to rekindle their magic moments. Can Lasse Viren of Finalnd, winner of both the 5,000 and 10,000 meters in 1972 and 1976, rise to the Olympic occasion again? Can Alberto Juantorena, Cuba's majestic "El Caballo," gallop to another gold in the 400 meters? What of Poland's Irena Szewinska, who has won seven medals in five events over four Olympiads?

There will be personalities to watch, such as Ethiopia's remarkable distance runner, Miruts Yifter, who was given erroneous directions to the starting line in Munich in 1972, and missed the Montreal Games in 1976 because of the black African boycott. He will be a favorite in the 10,000 meters and possibly the marathon. And there will be new stars, rising as meteorically as an Olga Korbut or a Comaneci.

But even though there will be good competition in many events -- as the Soviet media reiterates in a constant bombardment of rhetoric about how the "forces who want to ruin the Olympic Games" have failed miserably in "their unseemly political ends" -- there also will be a good deal of anticlimax.

In many glamour events, notably in track and field and swimming, this will be a wedding without the best man, or woman. Whoever wins the marathon -- perhaps Leonid Moseyev of the Soviet Union or East Germany's Waldemar Cierpinski, who startled the world by taking the gold in 1976 -- must wonder whether it would have been different if Bill Rodgers or Japan's Shigero Sou were in the race?

Does a gold metal mean anything to the winner of the long jump if he doesn't have to contend with American Larry Myricks. To the winner of the men's sprints and relays if they don't have to beat the Americans?

The athletes who are here are mindful of those who are not. Pietro Mennea, Italy's brilliant but temperamental sprinter, has kept his admirers in suspense as to whether he will run at all."The Games should be total, not with a whole slice of them absent," he said last week." "That's what makes me sick."

Such mixed feelings will be reflected in the opening ceremonies. Amid the glitter, there will be reminders of protest.About 20 countries plan to use Olympic flags rather than their national flags. Some will have only a token standard-bearer, holding aloft a plaque with the name of the team's national Olympic committee rather than its country.

In medal presentation ceremonies, some countries have asked that the Olympic hymn be played in lieu of their national anthems. Some athletes have indicated they might use the victory podium to protest the Afghan invasion, in defiance of Olympic rules.

The opening ceremonies and competitions will be much less lavishly covered than they would have been. Several boycotting countries have canceled television contracts. NBC-TV, which had planned to broadcast 150 hours of coverage, has a staff of 50 in Moscow instead of 600, and will televise a daily-highlights package of no more than 30 minutes, worked mostly into existing programs.

The hosts have spent hundreds of millions of rubles building and renovating facilities, stockpiling food that is in short supply for average citizens here, and sprucing up the city to impress the biggest influx of tourists in the nation's history.

Originally, 300,000 foreigners were expected to come, bearing the hard currency the Soviet economy so needs. Now that figure has been drastically reduced, although the Soviets refuse to give a new estimate.

They also avoid questions about commercial contracts with Western firms that were canceled because of the boycott -- Coca-Cola is one of the most conspicuous absentees -- and about revenue lost from television and other agreements that were terminated.

A month ago, the International Olympic Committee (IOC) was concerned that there would be technical breakdowns in the Games, snafus in running, timing and disseminating information about events, since some equipment could not be delivered because of Western embargoes.

Those fears have been allayed. Sports and communications equipment blocked from export by the United States has been obtained, in many cases by importing the same American-made goods through other countries.

The numerous judges, officials and technical staff prevented from coming to Moscow because of the boycott also have been replaced, but some competitors and team representatives think that there is now an overly high percentage of Soviets: 387 native referees and judges in the 21 sports, out of a total of 1,241.

The Olympic flame arrived at the steps of the Moscow City Hall on Gorki Street today just as the clock on the Savior's Tower at the Kremlin chimed 4 p.m. and the goose-stepping honor guard changed at the Red Square mausoleum where Vladimir Lenin, father of the Bolshevik Revolution, lies in state.

The Flame will burn overnight in the city council building, then be carried by premier Soviet athletes to the giant Olympic torch at the stadium, which will be ignited during the opening ceremonies. Meanwhile, other torches were dispatched by van to the cities of Kiev, Leningrad, Minsk and Tallinn, where various Olympic sports will be played.

"Quite honestly, the opening ceremony, to me, is the least important thing," IOC President Lord Killanin of Ireland said today. "What is important is that there should be good competition. Unfortunately, some sports will suffer. Others will not suffer at all. The experts will be in a position to assess the situation at the end of the Games."

In fact, as the Italian official foresaw, these will not be colossal Games. Only a colossal political event.