INDIO, Calif. (AP) _ Frank Sinatra has sued the National Enquirer for $22 million, alleging the tabloid fabricated a story that said a Swiss clinic injected the entertainer with a youth serum made of sheep fetus cells.

The suit filed Monday in Riverside County Superior Court also names as defendants the Clinic La Prarie in Montreux, Switzerland, and Stuart Goldfind and Susan Goldfind, the owners of a Cathedral City pharmacy where Sinatra or one of his employees apparently saw a copy of the Enquirer.

Sinatra, 69, lives in nearby Rancho Mirage, 100 miles east of Los Angeles.

The suit says the Oct. 23 front-page article falsely stated that Sinatra was admitted to the clinic Sept. 5 and that the next day he ''received 12 injections of live cells from black sheep fetuses.''

No one was available at the weekly tabloid's Winter Park, Fla., headquarters Tuesday night to comment on the suit, said a spokesman who refused to give his name.

Goldfind said Sinatra occasionally frequents his drugstore. He said he had not yet received a copy of the suit.

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LONDON (AP) - Princess Diana made an unscheduled appearance with her husband, Prince Charles, at a concert by Britain's Royal Philharmonia Orchestra to raise money for a concert hall in Reykjavik, Iceland.

Charles and Diana, 23, shook hands with Iceland President Vigdis Finnbogadottir after arriving at the Roya Albert Hall on Tuesday night for the concert, conducted by pianist Vladimir Ashkenazy.

The concert raised $1,260, organizers said.

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AUSTIN, Texas (AP) - Sadie the Great Dane is back home with New York Jets football player Johnny ''Lam'' Jones, who offered two Super Bowl tickets and a puppy for the return of the dog.

Jones, an Olympic gold-medal sprinter and former University of Texas star, offered the ducats and a Great Dane pup in a Sunday classified ad.

But Sadie turned up in a neighbor's yard, said a friend of the football player.

''The dog is such a friendly dog that he just follows anyone,'' said Gary Migilcutty. ''The people called and said it was in their backyard playing with their kids.''

Migilcutty said he did not know if Jones had to make good on his ticket- and-puppy offer.

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LOS ANGELES (AP) - Two stuntpeople were burned on the hands and face while filming a simulated vehicle explosion on the set of the ''Airwolf'' television series, the second accident this year involving the CBS-TV show.

Desiree Kearns, 28, and Chad Randall, 18, suffered second-degree burns in the accident Monday at Indian Dunes, Universal Television spokesman Ben Halpern said Tuesday.

Miss Kearns was admitted to the Burn Center at Sherman Oaks Community Hospital, where a spokeswoman said her condition was stable. Randall was treated at the Burn Center and released, Halpern said.

''The stunt had been rehearsed, all the safety precautions had been been taken, but the timing was off,'' Halpern said. ''There is an investigation to see if the mistiming was human or mechanical.''

In the first ''Airwolf'' accident this year, a Jan. 18 helicopter crash killed stuntman Reid Rondell, 22.

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DETROIT (AP) - A paperboy who prevented the rape of an 11-year-old girl and brandished a stick to hold her assailant for police says a congratulatory call from President Reagan ''had me smiling more than I ever smiled before.''

''I was froze. My mama says I was stunned,'' Collin Boatright, 14, said after his two-minute conversation Tuesday with President Reagan.

Today, the Michigan Association of Police plans to make Collin an honorary member and present him with a plaque and $500 savings bond.

The 4-foot-9 youth had just finished delivering The Detroit News on the city's east side Sunday when he heard screams from a vacant house.

A man had forced the girl to the second floor, where he was undressing her and himself, when Collin entered and asked him what he was doing, police said.

The man began to leave, but Collin said he threatened to hit the 6-foot-2 suspect with a stick if he didn't stop. Collin held him until police arrived.

''That must have been quite a moment, facing a man who outweighed you considerably,'' Reagan told the boy Tuesday. ''You have set an example for all of us.''