SEOUL, DEC. 26 -- In the wake of last week's decisions by Hungary and East Germany to participate in the 1988 Olympic Games in Seoul, officials in South Korea are optimistic the Soviet Union and China quickly will follow suit, setting the stage for the first boycott-free Summer Games since 1972.

"We have very good indications that all of the East Bloc is coming to Seoul, including Russia," said Park Seh Jik, president of the Seoul Olympic Organizing Committee (SLOOC). Referring to the acceptances by Hungary and East Germany, he added, "I am sure {the Soviet Union and China} will follow the precedent already made."

The 167 nations that belong to the Olympic movement face a Jan. 17 deadline for notifying the International Olympic Committee of their plans. So far, more than 100 countries have said they will attend the Seoul Olympics. Virtually all of the western countries, including the United States, announced in September and October their intention to send teams. Among those who have yet to do so are the Soviets and Chinese, plus their allies.

One reason for the increased optimism here is the outcome of South Korea's Dec. 16 presidential election, won by ruling party candidate Roh Tae Woo, who previously served as SLOOC president and sports minister. SLOOC aides now privately admit they had feared an opposition victory might have prompted a personnel reshuffling at the SLOOC and adversely affected delicate talks over North Korea's role in the Games.

Perhaps more important, SLOOC officials are breathing a sigh of relief that an expected wave of postelection protests has not materialized. For now, the country is relatively calm on the political front, and that's good news to the Olympic organizers. Widespread protests, or a military coup in the event of an opposition victory, would probably have sparked calls for the Olympics to be held in a more tranquil country and increased the likelihood of a boycott.

To the dismay of sports enthusiasts, boycotts have been almost synonymous with the Summer Olympics in recent years. In Montreal in 1976, some African countries stayed away; in 1980, the United States led a boycott of the Moscow Olympics because of the Soviet invasion of Afghanistan; in 1984, the Soviets led a retaliatory East Bloc boycott of the Los Angeles Olympics. The legacy of trouble is extended even further if the terrorist-marred 1972 Munich Olympics are added to the list.

Officials here are portraying the 1988 Summer Games as a last hope for keeping alive the Olympic spirit. "To save the Olympics in Seoul is to save the IOC and the Olympics in the future," said Park of SLOOC. "Perhaps God is providing us with a last opportunity."

But the specter of a boycott has haunted officials here as talks with communist North Korea remain deadlocked over sharing some of the Olympic sports. Pyongyang has insisted on co-hosting the Games and has threatened to call for a boycott unless its demands are met. Pyongyang has so far refused the IOC's compromise offer to stage all or part of five of the Olympic sports.

The communist bloc delay in notifying the IOC has been viewed as an attempt to bolster Pyongyang's negotiating position. But choices must be made with the deadline drawing closer. Seoul has been going all-out to smooth its relations with Pyongyang's allies, and the effort is showing some results. Hungary and East Germany are the first East Bloc countries to announce their plans to attend the Seoul Games, and it is believed their decisions were taken with the tacit consent of Moscow.

Officials in Seoul feel China's close ties with North Korea will not be a barrier to Chinese participation in the Olympics if Pyongyang stays away. Although Seoul and Beijing do not have formal diplomatic relations, their unofficial ties, particularly in trade, have warmed recently. Officials note China participated in the 1985 Asian Games in Seoul and predict the Chinese will be back in Seoul on Sept. 27, the day the Olympics begin.

The real danger of a North Korean holdout has little to do with sports. Seoul officials are worried that the erratic North Korean leader, Kim Il Sung, might sponsor a terrorist campaign before or during the Olympics, with the aim of embarrassing South Korea and inducing some countries to stay home. Because of this, plans for airtight security are almost as important in Seoul as the building of first-rate sports facilities.

"We are prepared for any eventuality that might happen before or during the Olympics," said Park of SLOOC. "We are committed to security."

The worries over North Korea appear to be well-founded. In 1983, Pyongyang was widely blamed for being behind a bombing attack in Rangoon, Burma, that killed three South Korean ministers. And just last month, the potential threat from Pyongyang was underscored when a Korean Airlines jet mysteriously crashed in the ocean off Thailand, killing all 115 people on board. Circumstantial evidence indicates a bomb was placed on board the plane by two suspected North Korean spies.

Despite this, SLOOC officials suggest that talks with Pyongyang could continue past the Jan. 17 deadline even if North Korea is firmly linked to the plane crash. "The Olympics must transcend all differences," said Park, who added SLOOC will "keep the door open {to North Korea} until perhaps the evening before the Olympics."

But other SLOOC officials are vague when asked if the deadline will be extended. "Although we will keep the dialogue open, time is running out," said Kim Un Yong, a SLOOC vice president and IOC committee member.