Challenger Anatoly Karpov came back -- reluctantly -- and played up to Move 57 before accepting defeat yesterday in Game 18 of the world chess championship match in Lyon, France. Defending champion Gary Kasparov's position had been technically invincible for 15 moves before the adjournment Saturday at move 41. It took the players less than half an hour (Kasparov only seven minutes) yesterday to play the concluding moves in a position that had obviously been intensely analyzed overnight. Kasparov now leads by one point, a margin that seems overwhelming as the match moves toward its final games.

Adjournment after 40 moves and overnight analysis, which have become an integral part of top-level chess, often with teams of experts using computer programs to analyze the adjourned position, came under fire in Lyon from the players themselves. At a board meeting of the Grandmasters Association, which represents the world's leading players, a proposal by former world champion Bobby Fischer to eliminate adjourned games was discussed. The board agreed it was a good idea, especially as adjourned games become more and more a struggle between computers rather than humans. It will research the situation and make proposals on how to implement the new system.

The GMA board also announced that the second cycle of six World Cup Grand Prix international tournaments, involving the world's top two dozen players, will start in October 1991 in Reykjavik and end in March 1993 in Barcelona. The association will also sponsor a speed chess circuit of four tournaments per year open to all grandmasters.

Kasparov's success in Game 18 can be traced back as far as his 17th move, Bd2, which put overwhelming pressure on the black pawn on a5 and led to his acquisition of a passed pawn on the b-file. In the final phases of the game, Karpov's earlier attempt to assault the white king's position backfired almost comically when the attacking rook was trapped in a cage of pawns -- white and black -- on the kingside.

In the final position, after exchanging h-pawns, Karpov can get his rook to the back rank to fight off the ambitious b-pawn by playing 57. ... Rh6+; 58. Kg2, Rh8. But then Kasparov can make the black king blockade the rook with 59. Rc7+, Kd8. The two black pawns on the seventh rank are then vulnerable if Kasparov cares to take them; Karpov cannot defend them with 59. ... Ke8 because of 60. Rc8+, capturing the white rook.

Karpov had made a bid for more time in a phone call requesting a technical timeout. It snowed in Lyon Saturday night and Sunday morning, six inches in the city and up to 12 in the hills outside the city where Karpov is staying, and Karpov (who is accustomed to the gentle winters of Moscow) said the snow made it impossible for him to reach the Palais des Congres where the games are played. Chief arbiter Geurt Gijssen drove out to demonstrate that the trip was possible and returned with Karpov, about seven minutes late.

Game 18 was the third decisive game in a row in a match that had been played to draws in 13 of the first 15 games. Each of the last three games has been won by the player having the white pieces and the advantage of the first move. Karpov will have white in Game 19, scheduled to begin today, and there is much speculation about whether he will be able to even the score again as he did in Game 17 last Wednesday. Such a win is almost a necessity, psychologically and tactically, if he is to keep any chance of winning back the title he lost to Kasparov in 1985.

The score is now 9 1/2 to 8 1/2 in Kasparov's favor, and he will keep his title if he reaches 12 points, as he can by drawing the next five games. Karpov can win the championship and the $1.7 million first prize by winning two of the remaining six games without losing any more. One more victory or a few more draws at this point will make Kasparov's advantage seem almost insuperable.