Anatoly Karpov won his fourth game from Victor Korchnoi Saturday in Baguio City, the Philippines, raising his lead in the world chess championship match to a score of 4 to 1. After Korchnoi resigned on his 40th move, facing a two-move checkmate, Karpov rushed from the Convention Center stage while Korchnoi stood, slump-shouldered and dejected.

The game began as a replay of the match's seventh game, in which Korchnoi managed to salvage a draw in what looked like a hopeless situation with Karpov's pawns marching down the center of the board. This time, in a tense, exciting middle game, Korchnoi managed to eliminate the dangerous pawns and to force the black king out into the center of the board, but it turned out that he was pushing Karpov where he wanted to go.

Shielded by two knights from the harrying of Korchnoi's two rooks, the black king marched deep into enemy territory, blocking escape routes for the white king, and the inactive black rook and the two knights joined forces to form a mating net.

In the final position, Korchnoi faced a checkmate in two moves: 40. PxN, R-N3ch; 41. K-R1, N-B7, mate. The only possible alternative would make the death-stroke come one move earlier: 40. K-R1, N-B7, mate.

Karpov varied from the system used in game seven on his eighth move, offering a second pawn sacrifice which Korchnoi declined, but the basic motif - black's sacrifice of a pawn to secure a threatening pawn center - was echoed until well into the middle game. By the 20th move, with three pieces trained on the white QBP, Karpov seemed to have Korchnoi in serious trouble. The challenger managed to exchange queens, mobilize his QB and launch an attack, but the problems simply became more complicated.

Korchnoi solved them one by one, but in doing so got into serious time trouble, a problem that has plagued him throughout the match. On his 30th move, with a bishop and pawn both being threatened, he bypassed 30. N-N5, which seems to promise at least to hold the position, and instead allowed Karpov to capture two minor pieces for a rook.

In the last 10 moves, apparently unaware that his king was about to be attacked, he wasted moves with two pawn captures and several checks that simply allowed Karpov to consolidate his position.

Some of Korchnoi's valuable time was wasted at the game's beginning in protests against the presence of Soviet parapsychologist Vladimir Zukhar in the first row of spectators. "I will give you 10 minutes to shift that man," said Korchnoi, who has accused Zukhar of trying to hypnotize him. "Otherwise I can do it with my own fist."

The referees answered the challenge by making all the spectators, including Zukhar, move further back. But by that time, his presence had apparently already had its effect on Korchnoi.

With a three-point lead, Karpov's victory in the match is now almost assured. The world championship and a $350,000 prize will go to the first player who wins six games. The loser's purse will be $200,000.