SEOUL, JAN. 12 -- The Soviet Union's announcement that it will attend the Olympic Games here in September, coupled with North Korea's apparent decision to boycott them, add up to a diplomatic triumph for South Korea, according to political analysts and western diplomats.

By gaining Moscow's participation and isolating Pyongyang from the rest of the world, Seoul has managed to bolster its global standing while undercutting and even embarrassing North Korea -- although South Korean officials and western observers warn that the North could hit back by attempting to disrupt the games through terrorism or by provocative actions along the DMZ.

South Koreans see the games as a showcase for Seoul's entry into the ranks of industrial nations and as proof that they, not the communist authorities in the north, are the legitimate government of the divided peninsula.

"In the diplomatic arena, it's over," said a jubilant senior official in South Korea's Foreign Ministry. "There is no longer any serious competition between North Korea and South Korea." The Korea Times said editorially, "There is no room for doubt that the Pyongyang boycott was motivated by jealousy of the prospering South."

In its statement early today, the North Korean Olympic committee said, "We will not participate in the Olympic Games, which South Korea attempts to host unilaterally." In an ambiguity that remains a topic of discussion in Seoul, the statement added that the North would review its position if talks were held on cohosting the games.

The Seoul Olympic Organizing Committee has refused to respond formally to North Korea's statement. But officials here said the North's bid to cohost the games remains unacceptable.

Although the officials say the North's boycott decision is final, they say that Pyongyang is still welcome to accept a longstanding compromise offer to host all or parts of five minor Olympic events. "We are open to talks up to the day of the Olympics," said one official.

Since the end of the Korean War in 1953, the two sides have largely fought their bitter rivalry on the diplomatic and rhetorical battlefield, although blood continued to be spilled in occasional military incidents along the tense demilitarized zone. Each side has sought international recognition as the legitimate Korea.

With its robust economy steaming ahead while political democratization also moves forward, the confident South counts diplomatic relations with 128 countries, while it says North Korea has ties with 101.

The importance that the South places on this numbers game was reflected by the front-page coverage that local newspapers gave to the announcement this week that Malta had agreed to reestablish relations.

South Korea does not have diplomatic relations with Moscow or with China, which is expected later this week to announce that it, too, will attend the games. The South Koreans hope the presence of Moscow and Beijing at the Olympics will lead to increased trade and eventual diplomatic ties.

"The Olympics will certainly mark a turning point in our relations with communist countries," the Foreign Ministry official said today. President-elect Roh Tae Woo, who made a campaign pledge to improve ties with China, reportedly is seeking to visit Beijing this year. Underscoring the stakes for the government in Seoul, Park Seh Jik, president of the Seoul Olympic Organizing Committee, called the games "one of the most significant events" in Korean history.

With a Jan. 17 deadline to join the games, 154 of the 167 eligible countries have said they will attend -- a record. North Korea is the only country to say it will stay away. Cuba earlier indicated it would follow the lead of North Korea.

Recalling North Korea's responsibility for a 1983 bomb attack in Rangoon that killed several South Korean ministers, officials here warned that Pyongyang could resort to terrorism in an attempt to discourage attendance. North Korea is already suspected of being behind the mysterious crash in October of a South Korean passenger jet in waters off Thailand.

"They've shown in the past that they're not particularly constrained by world opinion," said a western diplomat.