Several major newspapers, including The Washington Post, discovered yesterday that they had been hoaxed. All had run stories on the Fat Squad, a fictitious 24-hour surveillance service for easily tempted dieters.

The New York Post reported yesterday that Joe Skaggs, a veteran media prankster, had concocted the Fat Squad to point up the gullibility of the media and the public.

Skaggs, a self-described "multimedia artist" whose past scams include a celebrity sperm bank and a cathouse for dogs, said in a telephone interview from his home in New York City, "I understand and have empathy for the frustration of the people in the media . . . but that doesn't mean they can't do a better job."

Posing as entrepreneur "Joe Bones," the 41-year-old Skaggs mailed about 50 press releases to newspapers and networks in April. The releases advertised "cordial, but strict" Fat Squad "commandos" who would "supply all the moral support you need" for $300 a day.

Skaggs provided some reporters with names and telephone numbers of clients and commandos -- actually friends, many of them actors, who went along with the scheme. He told others that the Fat Squad contract guaranteed clients' anonymity.

Stories about the Fat Squad also appeared in The Philadelphia Inquirer, The Miami Herald and the New York Daily News, and were broadcast by the BBC and French television.

Skaggs, posing as Joe Bones, appeared Tuesday on ABC-TV's "Good Morning America" -- on which he had appeared about two years ago as the designer of fish condominiums. Yesterday morning host David Hartman apologized to his audience, saying, "We were had, in spades."