Victor Korchnoi has always considered 13 his lucky number, and on Friday the 13th he proved it winning his third game in a row from Anatoly Karpov and tying up the world-chess championship at a score of 5 to 5.

The match has been a sudden-death situation for Korchnoi since he lost game 27, giving Karpov a lead of 5 to 2, just one victory shy of the six victories needed to win the match. Now, after winning games 28, 29 and 31, Korchnoi has brought Karpov face-to-face with the same sudden-death prospect.

In the battle of nerves, endurance and sheer will-power - which have been as important in this match as technical ability - Korchnoi now seems to have an overwhelming edge.

Karpov's nervousness has visibly increased during the past 2 1/2 weeks, as his lead shrank from an overwhelming advantage to dead equality. At the same time, the size of the Soviet delegation supporting Karpov has continued to grow. In the beginning, it numbered 14, including a personal masseuse, a cook and a psychologist, as well as former world-champion Mikhail Tal who came as a journalist but has also been helping Karpov in the preparation of openings and end-game analysis.

Now the delegation has swelled to 29, including former astronaut Vitaly Sevastyanov, who heads the Soviet Chess Federation, and Victor Ivonin, a director with vice-ministerial rank in the Soviet Ministry of Sports and Culture. The size of the delegation may be an index of the pressure on the world champion.

"At 55 it's a lottery," a grinning Korchnoi said of his chances to win the title that most experts had concluded he could not win just two weeks ago. It was his third win in four games and his sudden resurgence had most of those experts predicting today that he would take the title he has covered for most of his 47 years.

Karpov, with just a rook and his king left after 70 moves, reached over and turned off the time clock to his right to signal he was resigning. He appeared powerless to halt an attack by Korchnoi's two pawns and rook. The isolated pawns were moving toward queening squares and Karpov was unable to halt both.

The two Russians, who make no secret of disliking each other, resumed play in the 31st game with Karpov opening his sealed 47th move. The two had adjourned the game Thursday, after five hours. The final moves are printed below.

The next - and possibly last - game in the 89-day-old title match is scheduled for today. Karpov could postpone the game until next Tuesday if he chooses.

But also scheduled today is action by the match organizer Florence Campomanes against Korchnoi's two American gurus. Campomanes Thursday night attempted to bar the two Americans - Stephen Dwyer, 28, of Kansas City, and Victoria Sheppard, 31, of Maryland - from the Korchnoi villa.

But in an almost predictable move in the circuslike atmosphere of the tournament, the chief Korchnoi aide overheard the organizer's telephone orders to police guards at the villa.

The aide, Raymond Keene, managed to talk the two Americans, currently on bail from an attempted murder conviction, past the guards into the villa.

"Tomorrow, I will take action," Campomanes said.