Champion Anatoly Karpov sealed his 41st move in Game 21 of the world chess championship in Moscow yesterday in a position that looked promising for his opponent, challenger Gary Kasparov.

If Kasparov wins when the game is resumed today, it will put the score in the 24-game match at 12-9 in his favor, and all he would need then is a draw to win the title. Karpov would have to win all three remaining games to hold the match to a tie in order to retain his title.

If Game 21 ends in a draw, Karpov must still win at least two games to retain the title.

Originally scheduled to be played on Tuesday, the game was postponed by Kasparov, who used the last of the three time-out options allowed him under the match rules. During his rest period, the challenger evidently studied innovations in the Queen's Gambit.

On his seventh move yesterday (after Karpov carefully avoided the Nimzo-Indian Defense that has brought him to grief three times in the match), Kasparov launched a surprise kingside attack before completing his development. One move later, he took the game into positions where no man has gone before -- at least on the world championship level.

Kasparov played as though he, not the champion, needed a victory merely to stay alive. Strictly speaking, he was taking unnecessary risks in a match situation where he needed only three draws to win the championship. But the gesture was typical of the flamboyant style that has won him a large following, in Russia and around the world.

Kasparov avoided castling and placed his king in the center on move 16, while the queens and most of the other pieces were still on the board, in order to concentrate his heavy artillery on the kingside. Karpov castled, but almost immediately had to undo most of his work, return the queen's bishop to its original square and send the queen's knight on an agonizing tour of the back spaces before sending it into action.

In the adjourned position, Kasparov has the initiative if not a clearly won game. Depending on Karpov's sealed move, Kasparov seems to have a choice of two strategies: a straight pawn-push down the opened center or a repositioning of his knights to press a double attack on Karpov's weak f-pawn. Judging from the position set up in his last few moves, he would probably prefer the first alternative.

The most Karpov seems able to hope for is a draw. In the current match situation, this would move his opponent a half-step toward the championship.

White Kasparov Black 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. fxe4Sealed