ONE WEEK FROM today, in the Philippines mountain resort of Baguio City, two men from Leningrad will sit down to begin the most dramatic chess confrontation since Bobby Fischer destroyed Boris Spassky (and himself) six years ago. Officially, it will be a match for the world championship between challenger Victor Korchnoi and champion Anatoly Karpov. Actually, it will be the last round in a long battle between Korchnoi and the Soviet Union.

Nobody knows how long the match will continue; the championship will go to the first one who wins six games, and there will be no limit on the number of draws. Four years ago, in the match that made him champion, Karpov beat Korchnoi by the smallest possible margin: 3 to 2, playing 19 draws in a total of 24 games. If the same ratio prevails in the Philippines, the match should last over four months and go to nearly 50 games. Much more likely is the prospect that one of the players will crack under pressure, sometime during the long summer, and the other will move in for an efficient kill. Which one will crack, which will win, is anybody's guess right now.

Comparison of the two players and examination of their records is suggestive but not conclusive for purposes of prediction. Challenger Korchnoi is 20 years older than his opponent; he will be 47 on July 23 - an advanced age for championship-level chess, which imposes stresses on a player, physical and mental, that demand an athlete's conditioning as well as the keen analytic mind of a research scientist.

But despite the age-differential, Korchnoi gives the impression of greater stamina; Karpov's frail appearance and pallor reinforce physically the frequent reports that his health is not good. Perhaps the most damaging of these statements is one by his friend and trainer Semyon Furman: "This thin and pale young man has a slightly phlegmatic appearance. Sometimes one has the impression it is difficult for him to move the pieces." A similar impression is given by his playing style, which tends to be rather passive and wary of complications when the opponent is someone he respects.

He should respect Korchnoi, who has won more games from him than anyone else, though (like everyone else) he has a minus score against the world champion. In the 35 games they have played, Karpov has won 7 and Korchnoi 6. Among the world's top 20 players, no other has beaten Karpov more than once.

Most of the time, Karpov's apparently frail health seem to have little effect on his chess; he has been losing an average of only two games per year since he became world champion, and he has kept up a very busy schedule, finishing first in almost every event he has entered. Curiously, one of the notable exceptions took place in the Philippines just two years ago; in July 1976, in Manila, he suffered one of the most devastating losses of his career, playing against Philippine grandmaster Eugenio Torre. His admirers blamed illness and the Philippine climate for his poor showing, which makes one wonder what he is doing back in Philippines in July starting the most crucial match he has ever played - his first defense of the title he took by default from Bobby Fischer.

In that same month, after two years in a Soviet purgatory, Korchnoi made the decisive step that has brought him to his present match with the champion: having won the IBM tournament in Amsterdam, he walked into a Dutch police station on July 27, 1976, and asked for political asylum. It was the beginning of a long, complicated gambit, played on and off the chessboard, and it now seems possible that it may work.

Gambits always involve a sacrifice for the sake of ultimate gain. In Amsterdam Korchnoi sacrificed his Soviet citizenship, looking ahead two years to the present match and seeing no clearer way to reach it. In the Soviet Union, since the end of 1974 when he lost his close match with Karpov and made some "unsporting" comments to the foreign press, Korchnoi had been practically a nonperson in his native land, allowed by Soviet authorities to participate in only one international chess event per year although he was universally recognized as one of the world's strongest players.

One reason Korchnoi wanted to play the upcoming match in the Philippines, according to his own public statements, is that there is no Russian embassy there; this does not guarantee the absence of KGB agents, but at least it makes it harder for them to operate. During the Belgrade match with Boris Spassky in late 1977 and early 1978 (one of the most surrealistic events in chess since Lewis Carroll slipped a sort of chess game into "Through the Looking Glass" between the lines, the press quoted charges allegedly by Korchnoi that the KGB was beaming microwaves at his head in an effort to scramble his brain. Spokesmen for Korchnoi later denied that he believed or made such charges, but considering what has happened at the U.S. embassy in Moscow, they don't sound totally impossible.

Whatever may be true about microwaves (or about the automobile accident that nearly killed exile Korchnoi a few days before his match with Spassky) his problems with the KGB date back all the way to 1961, according to associates and his autobiography. In that year, during the European Team Championships in Oberhausen, Germany, he invited a German woman to go to the movies with him and got a black mark in his dossier. The following year, at the world championship candidates' tournament in Curacao, he did something that may have been considered even worse; he visited a casino. When Soviet players return from overseas, they are summoned for an official discussion of what they did abroad. For Korchnoi, these sessions have always been specially intense.

Besides official signs of disapproval, there were others that seemed more "spontaneous." During the 1974 match with Karpov, for example, Korchnoi (whose reputation as a "bad boy" was already well-established) would be approached in the streets or on the telephone by "fans" who threatened him with violence if he won. The most remarkable gesture of all, since it involved losing a point for the Soviet Union, is told by one of his seconds, British grandmaster Raymond Keene, in "Korchnoi vs. Spassky: Chess Crisis," a book about the Spassky match published in England:

"At the 1970 Olympiad in Siegen he was deliberately sabotaged by his captain and team members who did not wake him up in time for the match against Spain, and even failed to contact him when he did not appear in the playing hall. It was only after his hour's grace had expired and he had lost by forfeit that he was woken up." If he had won the forfeited game (as he had every right to expect against a much weaker player), Korchnoi would have won an individual prize at the tournament.

Against such massive, bitter and organized opposition, Korchnoi has had no weapons but his own talent and (fitfully) the power of international public opinion - but with these (and particularly the former), he has managed to hold off the power of an outraged bureaucracy. After his defection, the Soviet press left the fact unreported for days; it was as though Joe Namath had popped up in Moscow, pledging his allegiance to the Workers' Paradise. The bureaucrats were stunned and at first didn't know what to say. When finally the news was reported to the Soviet population (which included thousands, perhaps millions of Korchnoi fans; he has a crowd-pleasing style, tough and adventurous), it came in the form of massive denunciations. "Traitor" was one of the milder epithets, and the chess bureaucracy solemnly announced that his career was washed up - then got to work trying to make that statement true.

The Soviet Chess Federation tried to have the title of grandmaster taken from him, and the International Chess Federation laughed the idea out of court; Korchnoi had not become a grandmaster because he was a loyal Soviet citizen, he had become a grandmaster because he was Victor Korchnoi. Then the Russians tried to make him ineligible to play for the world championship, but again they were told this right belonged to him as an individual. Finally came the ultimatum: No Russian player would participate in any international event that included Victor Korchnoi. This was a grim threat; an international tournament without Russians is just barely an international tournament. The same threat has been effective in thwarting the career of a Czech grandmaster, Ludek Pachman, who was on the losing side in the "Czech Spring" of 1968; Pachman supports himself with his books and he plays for a team in Germany's chess league, but he has been frozen out of international major-league chess competition because of a Russian boycott threat.

What worked on Pachman has not, so far, worked on Korchnoi. Because he came in second the last time the world championship was decided, he was automatically eligible to play in the elimination matches for the next championship, and Russians who refused to play against him would simply forfeit their games.

To get his crack at Karpov, Korchnoi had to play in three elimination matches. As luck would have it (and undoubtedly Korchnoi took a grim satsifaction in the way it turned out), all of his opponents were Russians. All of them played, and all undoubtedly ended up wishing they had been allowed to forfeit. With one exception, Korchnoi went through them like a brick through a window, nearly matching the spectacular record Fisher made in the 1971 championship preliminaries. Tigran Petrosian, a former world champion and an old enemy, was no problem at all; Lev Polugaevsky, who used to be a good friend, refused to shake hands with Korchnoi before the match began - then crumbled quickly, totally.

Spassky was more of a problem, not on the chessboard but in a bitter psychological war. He had also been a friend of Korchnoi's and was a semi-dissident, living outside of Russia but not renouncing his citizenship, and undoubtedly Korchnoi began with a certain amount of fellow-feeling - but this did not prevent his winning five and drawing the rest of the first 10 games in the match. In game 11, Spassky adopted a radically new strategy; instead of sitting at the table with Korchnoi between moves, he went off to sit in a private cubicle out of sight. Whether (as one theory had it) this was to make sure the microwaves didn't scramble both players' brains, defeating their purpose, or whether the effect was purely psychological, the result was devastating. Korchnoi lost four games in a row - two or three of them from positions which would have allowed a draw or even a victory if he had been in a normal state of mind. Even without the microwave hypothesis, the symbolism of the situation might explain the psychological tailspin. Korchnoi, sitting alone at the board on a stage in a packed Yugoslavian theater must have seen a micro-cosmic reflection of his personal situation: a nonperson, totally isolated, struggling against an unseen opponent all alone while the world watches. His commanding lead crumbled to the slimmest possible margin, a single point. Then he pulled himself together, played a draw, then another, and ended up with two more victories. It was a striking show of internal fortitude and a promising omen for the Philippine match, where there will be no vestiges of old friendship to stir up the subconscious.

Actually, Korchnoi need not have felt so isolated; his story is part of a larger one and he belongs to a growing brotherhood. Half a dozen notable chessplayers have left the Soviet Union in recent years; most have gone to Israel, but Spassky is in France and two players, Shamkovich and Lein, are now among the leaders in American chess. They are part of a still larger group. Among the people cheering for Korchnoi in his own language when he begins to play against Karpov will be men named Baryshnikov, Solzhenitsyn, Rostropovich. And if he wins, they will surely find his victory a fitting punishment for the way the Soviet Union treats men of talent who also have independent minds.