SEOUL, DEC. 2 -- South Korean President Chun Doo Hwan said today that evidence is mounting that North Korea planned the sabotage of a Korean Air jet over Burma Sunday.

The Korean Air jet disappeared while flying from the Middle East to Bangkok. South Korean officials said they believe the plane was destroyed in the air by a time bomb, killing all 115 people aboard.

Chun said preliminary Japanese investigations appear to tie North Korea to a still unidentified Asian couple who traveled on the jet on the first leg of its flight and then swallowed poison pills when questioned by police in Bahrain. One of them may have been a Korean resident of Japan.

"It is a plain fact that North Korea has intensified its provocative moves to obstruct the Seoul Olympics and the upcoming presidential election," Chun said.

The 1988 Olympics are scheduled to take place here next September, but the communist government in the north is trying to have some of the games moved to its capital, Pyongyang. South Korea's first direct presidential election in 16 years is set for Dec. 16.

Many people here said the bizarre and tragic saga of KAL 858 is likely to help ruling party candidate Roh Tae Woo in the election if North Korean sabotage is confirmed. In his campaign, Roh has emphasized the importance of stability and continuity to contain North Korean aggression.

"This will remind people of the threat," said former general Lew Byung Hyun. "Some of the candidates are very naive about North Korea and the possibility of unification."

Despite statements by South Korean officials, evidence of North Korean involvement remained tenuous and circumstantial tonight. Wreckage of the jet, believed to lie in jungle near the Burma-Thailand border, had not been positively identified.

The North Korean residents' association in Japan denied any involvement in the incident, calling it a "shameless conspiracy" by Chun and Roh to implicate North Korea and those sympathetic to it. Pak Che Ro, an official of the association, charged that South Korean candidate Roh "planned the incident" to help his chances in the election, correspondent Margaret Shapiro reported from Tokyo.

North Korean media have not reported the plane crash, according to officials here.

But Japanese police disclosed new details that appeared to link the two mysterious Asians to a Korean resident of Japan who was involved in a North Korean spy ring several years ago and has been missing since. Officials said the Asian couple, traveling on forged Japanese passports as father and daughter, would have had the opportunity to plant a bomb on the jet as it traveled from Baghdad to Abu Dhabi, where they got off.

The man was using a passport in the name of Shinichi Hachiya. When questioned about the incident yesterday in Bahrain, the man swallowed a poison pill and died four hours later.

Police said they believe the man may be Akira Miyamoto, an acquaintance of Hachiya, who is still living in Tokyo. Hachiya told Japanese police that Miyamoto borrowed his identity papers and personal seal in 1983 and his passport in 1984 and could have obtained a passport in Hachiya's name on one of those occasions.

Miyamoto is a Korean native who was linked to a North Korean spy ring in 1985, police said. Police found code books, disappearing ink and other signs of espionage in Miyamoto's apartment in March 1985, but they have been unable to locate him. Japanese diplomats brought photographs of the deceased passenger back from Bahrain to Tokyo tonight and police were expected to confirm Thursday whether the dead man was Miyamoto. Police were also expected to make a fingerprint check.

The young woman, meanwhile, remained in serious condition in a Bahrain hospital today and had not been questioned. She had traveled with a forged passport in the name of Mayumi Hachiya, and police said they do not know her identity.

{Takao Natsume, Japan's acting ambassador to Bahrain, said at a news conference in Manama, Bahrain, that the woman regained consciousness for about two hours, but slipped back into "an aggravated condition" without saying anything, The Associated Press reported.}

The two Koreas have maintained a hostile truce since their civil war ended in 1953, but North Korea has launched sporadic and unpredictable attacks against the South during that time. In 1983, four Cabinet ministers and 13 other South Koreans were killed by a bomb in Burma. Burmese officials concluded that North Korean agents were to blame.

In October, the North Korean Navy sank a South Korean fishing vessel, apparently without provocation.

New details emerged today about the two passengers' travels through the Middle East and the way in which they came under suspicion.

Sitting in the seventh row aboard the KAL flight, the two acted strangely, never answering flight attendants' questions and consuming only water, according to Korean Air crew members who remembered them.

The two were among 15 passengers who left the plane in Abu Dhabi, officials here said.

South Korean diplomats and airline officials began concentrating on the 15 passengers who disembarked in Abu Dhabi. The "Hachiyas" stood out because almost no Japanese passengers fly that route, officials said. Suspicion heightened when it was learned that they had continued to Bahrain without having left the Abu Dhabi airport.