The five-month-old match for the world chess championship was ended suddenly today by the president of the International Chess Federation, setting off widespread speculation that the unprecedented action was designed to save defending champion Anatoly Karpov from defeat.

"The match is over without a decision. A new match will be played from scratch, 0-0, starting from September 1985," said federation president Florencio Campomanes at a tumultuous press conference interrupted by objections from both Karpov and challenger Gary Kasparov.

Campomanes' unexpected move created a sensation in this capital, where chess is taken as seriously as politics. It appeared so arbitrary that most Soviet and foreign observers here saw it as a moral victory for the 21-year-old Kasparov, who had defeated the world's best players in an international elimination tournament to reach this challenge round.

Kasparov had won the last two games in the marathon match to narrow the score to 5-3, with draws in 40 other games. Karpov, who led 5-0 in November and needed only one more victory to retain his title, had become progressively more exhausted under the match's intense pressure.

Campomanes said he was halting the match because it "has exhausted" the players as well as "all those connected" with it. But his explanations were confusing and contradictory. At one point, he declared that he had been uncertain of his action until the press conference. "Until reaching this podium I did not know what I was going to do," he said.

However, the Soviet news agency Tass had reported Campomanes' decision 12 minutes before the press conference started.

The federation president also seemed to contradict himself when he said that the Soviet chess federation "agrees with my decision." The remark suggested that Campomanes had communicated his views to the Soviet chess authorities in advance.

In announcing his decision, Campomanes said he had the "consent" of both players, a point that Kasparov angrily refuted.

The 33-year-old Karpov, who has been world champion since 1975, when Bobby Fischer of the United States declined to defend his title, is a darling of the Soviet chess establishment. Chess is the most popular game played here, and championship players are privileged members of the Soviet elite, with exceptional prestige and influence.

Moreover, Karpov was seen here as a man who valiantly defended the nation's honor when he defeated Viktor Korchnoi, a Soviet defector, in a 1978 title match. Karpov holds the country's highest civilian decoration, the Order of Lenin.

Karpov, a Russian, is a member of the Communist Party. So is his youthful challenger, who is part Jewish and part Armenian. Campomanes, whose federation groups the national chess bodies of more than 120 nations, is a Philippine citizen.

In an effort to mollify Kasparov, Campomanes ruled today that the players should split the 72,000-ruble (about $85,000) prize money evenly. Normally, the winner was to have received 45,000 rubles.

Today's press conference, attended by more than 150 journalists, was marked by uproar rarely seen in the Soviet capital. At one point, after both Karpov and Kasparov announced that they were eager to continue the match, Campomanes adjourned the session for a private conference with the two players to reconsider the decision.

However, Karpov refused backstage to meet privately with Kasparov and Campomanes. Instead, about 15 persons took part in the deliberations, which lasted an hour and 38 minutes.

A participant in the private meeting indicated that Vitali Sevastianov, a cosmonaut who is president of the Soviet chess federation, was pressuring Kasparov to agree to a joint statement calling for a new title match on Sept. 1.

Kasparov refused to sign the statement and to join Campomanes, Sevastianov, Karpov and others for a picture-taking ceremony.

When the press conference resumed, Campomanes said that the world champion "accepted" his decision to restart the match in September but that the challenger only agreed to "abide" by the decision.

Earlier, Kasparov had denounced Campomanes' press conference as a prearranged "show" and said he was being prevented from playing when he had his first real chance to win.

The outburst by the challenger, who seemed on the verge of a spectacular comeback, came after Karpov appeared in the hall midway through the press conference. The champion made his entry just as a reporter asked Campomanes to comment on reports that Karpov was so physically and psychologically exhausted that he was unable to continue.

"You asked the question at the right time," Campomanes replied. "Mr. Karpov is standing right behind you." The champion, who has lost more than 22 pounds since the match began in September, appeared pale and exhausted. But he marched to the dais to declare, paraphrasing Mark Twain, "I have to tell you that rumors about my death are somewhat exaggerated."

Karpov continued: "We can and should continue this match because the proposal to terminate it and start again from scratch does not suit me. I believe that we should continue our match on Monday. I believe that Kasparov will support this proposal and there should be no problems."

"Gentlemen," injected Campomanes, addressing the press, "now you know that what I told you earlier is true." Campomanes had said that the champion was eager to continue the match, that he was "well and he appealed to me to continue with the match to the very end."

"Many of you know that I am a very good friend of Mr. Karpov," Campomanes continued. "You are right. But this has nothing to do with what I feel is best for chess in the world."

With Karpov on the dais, journalists clamored for Kasparov to join the officials there. The challenger had arrived before the press conference and was seated in a back row.

Clearly angry, Kasparov moved to the dais and, pointing a finger at Campomanes, demanded an explanation of "why are we having this show."

"I will clarify my question," Kasparov continued. "You said you came here 25 minutes after a walk with the world champion and that he was against the termination of the match. You already knew perfectly well my point of view. I was also against terminating the match. Despite that, you announced that the match is terminated. What is all this? I do not understand."

Campomanes, taken aback, responded by saying that he personally believed what he was doing was in the best interest of chess. "Now, however," he continued, "I am in a very happy position right now.

"If the two players wish to play to the very end I will consider in a conversation with the two of them alone" a reconsideration of the decision, Campomanes added. "Let's have 10 minutes inside."

But Kasparov continued with his statement before he and others left the stage: "I want to say what I think. I do not demand the continuation of the match because I believe that I can easily win on the account that the world champion is not feeling well. He is here and he is able to play, we can all see that. But simply, for the first time in five months there are some chances, some chances, in percentage about 25 to 30 percent, and now they are trying to prevent me with endless delays and timeouts. The match should continue."

Karpov responded by saying, "We need a break now to calm down and after that we will have a decision."

After the backstage conference, Campomanes read a brief statement: "The world champion accepts the decision of the president and the challenger abides by the decision of the president."

A source present at the backstage meeting said Campomanes had threatened to resign if his decision was not accepted.

After the press conference, Kasparov rejected Campomanes' right to terminate the match. "I am perfectly healthy and ready to play. Why play chess if the president can take these decisions at any moment? Why not have him appoint the world champion?"

Campomanes, who had flown to Moscow four days ago at the request of Karpov's doctors, said the rules for the rematch would be set by a federation congress in Graz, Austria, in August.

The Karpov-Kasparov match was an open-ended tournament with games played on Mondays, Wednesdays and Fridays. Often, however, these games were adjourned and continued the next day, with both players and their advisers spending much of the night analyzing their positions and possible solutions.

An overconfident Kasparov had started the match impetuously last fall, hoping to gain quick victories against the advice of his experts. After the drubbing he suffered in the first 12 games, when the score was 4-0 in Karpov's favor, Kasparov adopted his advisers' tactics and began to play for time.

This approach had strategic merit, since the 21-year-old challenger could count on his stamina to outlast the slightly built Karpov.

Kasparov's change of strategy resulted in 40 draws -- a record number in a world title match. It also exhausted the champion. Chess experts said Karpov's play was steadily declining while the challenger's play and self-confidence were on an upswing.

Since Kasparov's two consecutive victories last week, the match's Soviet organizers delayed scheduled games until Campomanes arrived and called for a time out.

Kasparov had objected to the delays. Following the press conference, he questioned Karpov's stated readiness to continue the match.

"I don't know if he is talking sincerely about his desire to play. But this reminds me of a well-rehearsed performance in which everybody knows his own role," Kasparov said.