World champion Anatoly Karpov came from behind yesterday in Moscow and held a draw in a chess game that had looked lost when it was adjourned Thursday night. Challenger Gary Kasparov wiped out his superior position with three weak moves in a row, including a final move that exposed his king to a deadly discovered check -- a sequence that will be called a blunder. He then quickly agreed to a draw.

Expert observers on the scene in the Tchaikovsky Concert Hall were stunned by the rapid change in the situation. They had almost unanimously said that Kasparov would win when play was resumed, and some of Karpov's strongest supporters had pronounced his position hopeless. But in four moves, Karpov was able to mobilize his knight and bishop into threatening positions that would force Kasparov to move his king out of action or risk losing a vital pawn.

"I cannot explain it," grandmaster Yuri Averbakh told a reporter. Josif Dorfman, one of Kasparov's seconds, merely raised his eyebrows and said the situation was "very interesting" when the players unexpectedly agreed to a draw. Observers in Moscow conjectured that Kasparov and his advisers found unexpected weaknesses in the position during their intensive overnight analysis.

Although the result was a moral victory for Karpov, it leaves him still in an almost impossible position. The score now stands at 11 1/2-9 1/2 in Kasparov's favor. He need only draw two more games or win one to take the crown. Karpov can allow only one more draw and must win two of the three remaining games to tie the match and keep his title.

In the final position, Kasparov faces a hard choice. He can move his king out of action (for example with 45 Kd2, Nc4ch; 46 Ke1), abandoning all hope of an effective attack. Or he can defend his endangered b and d pawns with 45 Kc3, after which he faces a draw by repetition of moves (45 . . . Nb5ch; 46 Kd3, Na3ch, etc.). What he cannot do is keep his king in a strong central position with 45 Ke3. Karpov would reply with Nc2ch, capture the undefended b-pawn and have winning chances with a strong queenside majority and passed pawns on both sides of the board.

This game does not seriously undermine Kasparov's chances of winning the championship. But it leaves chess fans wondering what might have happened if he had played 42 e5 or 42 a4 rather than the puzzling move he actually made.

White Black Kasparov Karpov

1. d4d5 2. c4e6 3. Nc3Be7 4. cxd5exd5 5. Bf4c6 6. e3Bf5 7. g4!Be6 8. h4!Nd7 9. h5Nh6 10. Be2Nb6 11. Rc1Bd6 12. Nh3Bxf4 13. Nxf4Bd7 14. Rg1g5 15. hxg6ephxg6 16. Kd2!Qe7 17. b3g5 18. Nd30-0-0 19. Rh1f6 20. Qg1Nf7 21. Qg3Qd6 22. Qxd6Nxd6 23. f3Rdg8 24. Nc5Kd8 25. Bd3Bc8 26. Ne2Na8 27. Bh7Rf8 28. Rh6Nc7 29. Ng3Nf7 30. Rh2Ne6 31. Nd3Ng7 32. Rch1Ke7 33. Nf2Rd8 34. Bf5Rxh2 35. Rxh2Nxf5 36. gxf5Rh8 37. Rxh8Nxh8 38. e4Nf7 39. Ng4Nd6 40. Ne3dxe4 41. fxe4b6 42. b4Ba6 43. Ng4Nb5 44. Kd3Na3ch Drawn