One fact is becoming evident as the World Chess Championship finishes its first quarter: If defending champion Gary Kasparov offers his opponent a gift, the opponent should beware. In Game 6 in New York last night, Kasparov's gift to challenger Anatoly Karpov was a pawn. This did not cost Kasparov much, because he got a chance to exert tremendous pressure in exchange.

It took three moves, beginning with 25. c4, to complete the transaction, and at the end of this process, Kasparov was shy one pawn, but his pieces, formerly blocked and cramped in awkward positions, were suddenly aimed right at his opponent's kingside.

Swallowing one of Kasparov's pawns can cause indigestion, but Karpov accepted the sacrifice -- somewhat reluctantly. He had no better choice, because Kasparov would have been able to switch his pieces to the kingside anyway, while also paralyzing the weak black pawn on d6. Karpov seemed to be holding his own and heading for a draw for the first 31 moves. Then Kasparov found some strong attacking moves, and by the time the game was adjourned, he was looking for a win, while Karpov seemed to have chances for a draw.

In this game, Karpov abandoned the Zaitsev Variation he had played in earlier games in favor of 9. ... Nd7. His next move, 10. ... Bf6, put pressure on white's pawn center, preventing normal development of white's queenside pieces.

Karpov has played this variation lately with mixed results, and Kasparov, who arrived four minutes late, losing time on his clock, seemed ready for it. His sequence of four moves starting with 11. a4 was the strongest continuation currently known to chess theory.

Karpov managed to cover his weak pawn on b5 quite efficiently but could not prevent the long knight maneuver, beginning with 18. Nh2, with which Kasparov was able to swing his knight into a strong offensive position. All this would not have led to anything if Kasparov had not made the brilliant pawn sacrifice with 25. c4. After Karpov accepted it, Kasparov activated his white-square bishop, putting pressure on the weak pawn on f7.

Still, Kasparov's attack seemed to be dying until he came up with a brilliant two-move continuation of the attack: 32. Rf3, and 33. Ne3. After this, the game was completely in his hands. Karpov was doomed to a passive defense and was ready to give up his queen with 35. ... Ra7. Kasparov could have played 36. Rxf7, Qxf7; 37. Bxf7, Rxf7, but had seen that Karpov might have built a fortress that would not allow him to transform his material advantage into a win because of reduced pawn material. Instead, the world champion took full control of the white squares with 36. Qb3 and soon penetrated black's position with his heavy pieces.

After move 40 Kasparov could have sealed his next move and found 41. Qc8 more attractive with the idea of attacking along the g-file with 42. Qg4ch, Kh6; 43. Rg3.

If the game ends in a draw, Kasparov will be ahead in the match by a score of 3 1/2 to 2 1/2. It is scheduled to resume tonight at 5:30 p.m.

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