World champion Anatoly Karpov abandoned a promising but speculative position and offered a 23-move draw yesterday in Game 18 of the world chess championship match in Moscow. Challenger Gary Kasparov, who is leading in the match by one point, thought for a half-hour before accepting the offer. With only six games remaining and a score of 9 1/2 to 8 1/2 in his favor, each draw adds to Kasparov's psychological and strategic advantage.

Despite its short duration and drawn ending, the game was not dull or routine. Karpov played a Sicilian defense but pointedly avoided the innovative variation that plummeted him to a disastrous loss in Game 16 last week. His style in this game was more aggressive than usual, as it has to be in the match situation, while Kasparov, who needs only a series of draws, retrenched into a defensive posture. But after lining up his pieces for attack and clearing lines in the center, Karpov hesitated to plunge into the kind of middle-game complexities that the tactically sharp Kasparov has turned against him in previous games.

White/Black -- Karpov/Kasparov

1. e4c5 2. Nf3d6 3. d4cxd4 4. Nxd4Nf6 5. Nc3a6 6. Be2e6 7. 0-0Be7 8. f40-0 9. Kh1Qc7 10. a4Nc6 11. Be3Re8 12. Bf3Rb8 13. Qd2Bd7 14. Nb3b6 15. Bf2Bc8 16. Bg3Nd7 17. Rae1Bb7 18. e5Rbd8 19. Qf2Rf8 20. Be4dxe5 21. fxe5Nc5 22. Nxc5bxc5 23. Bf4Drawn