"The 70-year-old marathon is over." So declared Jim Thorpe's daughter Charlotte at a Los Angeles ceremony yesterday restoring the gold medals won in pentathlon and decathlon at the 1912 Stockholm Olympics, and taken away when it was learned Thorpe earlier had accepted $2 a game to play baseball.

International Olympic Committee President Juan Antonio Samaranch officially returned the medals (actually replicas). Present were six children, including William Thorpe of Arlington, and many grand- and great-grandchildren of the athlete of the 1901-50 half-century, dead 30 years now.

"I'm sure father is with us here today, and he would say one word: thanks," said William. A victory for "the Indian people of America," said Jack Thorpe of Shawnee, Okla., chief of the Sac and Fox tribe. "I can't believe it, I've been working on it all my life," said oldest child Gail Thorpe, 63 . . .

The U.S. Olympic Committee, meanwhile, joined with the Amateur Basketball Association- USA to reaffirm support of Indiana's Bob Knight as U.S. coach in the sport for the 1984 Games. Critics have called for Knight's removal because of his demeanor during the Pan American Games in 1979.