NEW YORK, OCT. 12 -- Game 3 of the world chess championship here has been postponed at the request of challenger Anatoly Karpov, who lost the previous game in the match to reigning champion Gary Kasparov. Originally scheduled to start at 5:30 p.m. today, the game was rescheduled for the same time on Monday, with Karpov playing the white pieces.

A request for postponement can be read as an admission that Karpov was seriously shaken by his loss in Game 2. In deciding whether to postpone, he had to balance the benefit of three more days to prepare against the detriment of showing vulnerability.

One reason for today's postponement may well be Karpov's need to recover from the blow that comes with a defeat such as he suffered on Wednesday, when Kasparov tore gaping holes in the Zaitsev variation of the Ruy Lopez -- for years one of Karpov's most reliable responses to a king's pawn opening.

Another, more practical reason is certainly his need to consult with his team of experts and find new ways to strengthen that line of defense. The fruits of the challenger's extra time for preparation may be shown in an especially tough attack on Monday or in a fresh look at his defense philosophy on Wednesday when he is to play black.

It is possible for Karpov to avoid the variation with which he lost simply by choosing another opening, such as the French or the Sicilian Defense, against 1. e4, but such a choice would take him out of his most familiar territory, deprive him of the benefits of long, hard study and perhaps send him into another trap carefully prepared by Kasparov. It would also mean, psychologically, a concession that he had lost control of an important part of the battlefield.

Each player is allowed during the 24-game match to have three postponements, usually requested when a player is ill or fatigued (usually late in the match) or has endured a particularly disturbing defeat. If necessary, a player can allow his opponent more than three postponements. During a 1977 candidates' match in Reykjavik, Iceland, Boris Spassky had appendicitis and was still unable to play after taking his three postponements. His opponent, Vlastimil Hort, was asked to allow Spassky another week to recover, and he did so as a gesture of goodwill. After recovering, Spassky promptly defeated him.

Sometimes postponement requests are made for reasons that might seem frivolous but that some players take quite seriously. Kasparov is now known to have tried to manipulate his 1987 match with Karpov in Seville, Spain, to start at a time when Karpov's biorhythms were low. In the light of such preoccupations, it may be significant that a game played in New York on Oct. 12 would have gone over into Oct. 13, Moscow time. Kasparov considers 13 his lucky number, and Karpov would try to avoid playing on that day. In the same vein, Karpov's horoscope for today mentions a "waiting game." This kind of game is not appropriate with the white pieces, which Karpov was scheduled to play, but he might have decided to put the whole match into a "waiting game" mode.

The postponement request arrived in a telephone call to chief arbiter Geurt Gijssen from grandmaster Lajos Portisch, Karpov's second in the match, at 11:53 a.m., seven minutes before the noon deadline. A letter signed by Nikolai Krogius, the chief of Karpov's delegation, was handed to Gijssen at 12:07 p.m., and the timeout was officially declared.

When he received Portisch's phone call, Gijssen humorously insisted that the Hungarian grandmaster must prove his identity by singing a song over the telephone. In recent years, Portisch has added a musical career to his chess activities, singing frequently in recitals and on the radio, mostly in Hungary. Fellow grandmasters have complained that during tournaments he keeps them awake late at night and early in the morning by singing in his hotel room.

Lubomir Kavalek is a chess grandmaster. Joseph McLellan is a Washington Post staff writer.