The three major American television networks have expressed serious interest in buying broadcast rights that would pay the cost of the "post-Olympic international sports festival" that the United States, Britain and others have decided to organize, U.S. officials said today.

Lloyd Cutler, leader of the U.S. delegation at a conference exploring the feasibility of alternative games for athletes who boycott the Moscow Olympics, told a press conference that the 12 nations participating had concluded that the events could be "financed successfully by the sale of television rights."

Cutler, who serves as special counsel to President Carter, said some of the participants in the two-day conference here had expressed willingness to finance alternative games. He refused to estimate how much they would cost or to say which countries were involved. They presumably include the three organizers of the Geneva meeting -- the United States, Britain and Australia.

David Wolper, the producer of the television series "Roots" and an adviser to the U.S. delegation, said, "from my knowledge of network matters, all three networks have considerable interest in covering these games." Wolper, a member of the Los Angeles Olympic Committee, negotiated the sale of the 1984 Olympics in Los Angeles to ABC television for $225 million. NBC paid the Soviets $87 million, but will recover most of it under a Lloyds of London insurance policy.

Cutler offered the presence of Wolper in the U.S. delegation as proof that the alternative games "would pose no threat to the future of the unitary Olympic movement, a future to which all the governments present at this meeting are as dedicated as any governments in the world." The events, Cutler said, "would not in any sense by counter-Olympics."

There would be no special medals, no flag ceremonies and no special anthem for the post-Olympic games. "The emphasis will be on athletes rather than nations," he said.

Cutler said the conference came up with four to six potential sites for alternative games to be linked by television satellite. He would not name them, but speculation centered on Kenya, Canada, Australia and the United States, all conference participants. Boston, Houston and New York have volunteered to host such games.

U.S. officials said that the hope was to hold five or six "clusters" of games covering most of the 21 Olympic sports over a three or four-week period. The games would start in mid-September, U.S. officials said.

The idea is to "build up" many of the traditional post-Olympic competitions already scheduled for athletes "on their way home from the games," U.S. officials said. They conceded that there is a possibility of a counter-boycott of those events by Soviet-bloc athletes.

Cutler said that a working group established here would subdivide itself and "fan out" to talk with other countries. The Dutch and British conference participants, for example, would talk to the sports ministers of the nine countries in the European Economic Community.

U.S. officals estimate that at least 50 countries intend to boycott the Moscow Games, but it is too early to estimate how many are ready to take part in the alternative games.

The Americans stressed that the importance of getting athletes to honor the boycott is to prevent the Soviets from saying: "The people are here notwithstanding the stand of their reactionary governments." To make sure the athletes follow the lead of their governments, Cutler said, "we feel it is our duty" to provide "worldclass" alternative events.