Gary Kasparov, pushing his opportunities too hard, blundered away a rook, a game and probably his world chess championship yesterday in Seville, Spain.

To keep it, he must win the 24th and last game, which begins today. He is in a desperate situation, and if his self-confidence has not been totally shattered by his loss to challenger Anatoly Karpov, he should make it one of the most wildly aggressive in the long series of championship games between the two players.

In an exclusive telephone interview after his victory yesterday, former champion Karpov agreed that he had "received a present" when Kasparov overextended himself.

"But," he added, "it is the first time in three matches."

His response, a refutation of an attacking combination by Kasparov, was one of the more brilliant moments in the 119 championship games these two men have played, a series now tied at 59 1/2 points apiece.

Despite the hours he spent working on this game with his team, Karpov said, the winning move was his own spontaneous discovery: "In our analysis, we saw many themes where the queens would be attacked simultaneously, but this one I found over the board."

Karpov is too much of a gentleman to say it bluntly, but what overthrew his opponent yesterday were the young champion's perennial qualities -- or perhaps flaws -- of aggressiveness, greed and overoptimism. In brief, he spurned clear prospects of a draw and played for a win that was just out of reach.

After resigning the game with a wry grin, Kasparov buried his face in his hands. Then he rushed from the stage into his private dressing room, still hiding his face, while applause rumbled through the Teatro Lope de Vega, the elaborately baroque opera house where the games are played.

Karpov was also visibly moved by the sudden reversal of an unpromising situation, and wept as he left the playing hall. His aides -- who had seemed optimistic on returning to the theater to begin the game's second session -- said he had stayed up all night planning his attack.

Besides the championship title, stakes in the match are $1.35 million for the winner and $812,500 for the runner-up. If the final score is tied, the prize money will be divided evenly between the two grandmasters.

The match score now stands at 12 to 11 in Karpov's favor, with 16 games drawn and four victories for Karpov against three for Kasparov. A Karpov victory or a draw in the game that begins today will return to Karpov the title he held from 1975 to 1985. A Kasparov victory would tie the match at 12-12 and leave him badly shaken but still champion. No player in the history of the world championship has ever managed to come from behind like that in the final game of a match.

Kasparov's plight now echoes that of Karpov at the beginning of Game 23. "He knows he is forced to win," one of Karpov's team members told the press while the game was still in progress yesterday.

Karpov insisted that he had a slight advantage when Kasparov made his blunder, but he was behind on the clock. By Move 50, he said, "Kasparov started to play on my time trouble, trying to exploit the advantage that I had only three minutes and he had seven for our last six moves. But after he played 50. R7f3, I used two minutes out of my remaining three to calculate, and then I saw the refutation that led to my winning position."

On Wednesday evening, he had thought for seven minutes before sealing a very strong move (41. Rg1), which killed two birds with one stone. It not only prevented any possible rook sacrifice on g2, it also obviated the strong attacking move 41. ... Qh4, which Karpov would have met with 42. Be1, winning the exchange. Once he had forestalled these direct threats, Karpov was out of immediate danger, and his other rook was free to go off and play a disruptive role in Kasparov's territory, tying down some of the champion's attacking pieces.

After 48 moves, the position was still in balance and Karpov had avoided a trap. Had he become greedy for a pawn with 48. Rxe5, then after 48. ... Bd6; 49. Re6, R7f3, Kasparov's breakthrough attempt would have worked because of mating threats on h2.

It was exactly this kind of combination that lured Kasparov to his doom later in the game, in a position where the combination simply didn't work. He must have felt quite optimistic about his chances, since he turned down the option to play 49. ... R1f2, which would most likely have been met again by 50. Be1, implicitly offering a draw.

Instead, Kasparov launched into the "winning" combination without realizing that Karpov might be ready with a disabling counterpunch. The combination beginning with 50. ... R7f3 was simply a blunder -- so once again, one of the players, expecting to be brilliant, looked like a mere human being. Karpov's refutation came with 53. Bh6 -- a move Kasparov himself would have enjoyed playing, since he always likes to answer one punch with another.

Kasparov appeared stunned when he saw Karpov's Move 53, and lost valuable minutes on his clock considering his response. After that move, it was clear that black must lose material. He was unable to play 53. ... Qf6 because of 54. Bg7ch.

As his position grew more insecure, Kasparov began to fidget in his chair and nervously raised his hand to his head, almost as though warding off a blow. At one point near the end of the game, he knocked over his own bishop and a white pawn while advancing a piece.

In the final position, black has made his rook vulnerable to capture by white's king or bishop, and he resigned after seeing that white would not fall into this final trap. After either 54. Bxg1 or 54. Kxg1, the move 54. ... e2 puts the black pawn in an unstoppable position to become a queen.

To counter this threat, white would most likely play 58, Bb4. For example, 58. ... Rb1; 59. d6, Rxb4; 60. d7, and it is white who queens first.

Asked after the game whether it is harder to fight for the championship or to try to hold it, Karpov answered, "Who knows? May I give you the answer after tomorrow's game?"

Grandmaster Lubomir Kavalek contributed to this report.