NBC, agreeing to an unusual "risk-sharing" plan, has won the bidding among U.S. networks to televise the 1988 Summer Olympics from Seoul, South Korea.

In New York, the International Olympic Committee announced that NBC will pay between $300 million and $500 million for the broadcast rights. The "sliding-scale" payments will depend on gross sales of television time to advertisers.

Arthur Watson, NBC Sports president, said in a statement, "With the prospect of more nations participating, these Games hold the promise of being the best all-around competition of any Summer Games in history."

NBC plans 180 hours of coverage. "Many efforts have been made by the Seoul Organizing Committee (SLOOC) to improve the schedule so that we can telecast many events in prime time," Watson said. "We anticipate 80 percent to be live."

At first, the SLOOC had anticipated bids from NBC, CBS and ABC of up to $600 million. "It will be a record contract," one SLOOC official predicted last month. But reportedly, in the first round of negotiations, no network bid higher than $325 million.

A major reason for the low bids was the 14-hour difference between Seoul and the United States' Eastern time zone.

ABC Sports, which paid $225 million for TV rights to the 1984 Summer Olympics in Los Angeles and will pay $309 million for rights to the 1988 Winter Games in Calgary, Alberta, said, in a statement, that it felt "strongly that the Calgary Games are a more valuable property . . . (we) would have welcomed the opportunity to televise the Seoul Games, but offering more than we did would have been imprudent."

But NBC's Watson said, "At 10 a.m. in Seoul, it is 8 p.m. the preceding night in the United States, and at 9 p.m. in Seoul, it is 7 a.m. in New York. We can show a lot of events in prime time and late at night and we can also show events during the 'Today Show.' "

NBC, which last broadcast a Summer Olympics in 1964, from Tokyo, for the price of $1.5 million, had bid $87 million for the 1980 Summer Games in Moscow. The network then took heavy losses when it had to forgo its plans for extensive coverage because of the U.S.-led boycott of western nations.

Watson said NBC will be covered by insurance in the event of another boycott by the United States, the Soviet Union or any other major participant.

"We absolutely anticipate a profit," Watson said. "We're realistic and we know what the Olympics are worth."

"We are quite satisfied with the minimum ($300 million) that has been provided, not only because it is an astronomical number but also because we don't think it's the real number," said Richard Pound, head of the IOC's television rights committee. "We are confident it will be higher, up to the maximum."