Capriati Begins Treatment Program : Tennis: She will deal with substance abuse at rehabilitation center. Arrest costs her endorsement deals.

Jennifer Capriati will be treated for substance abuse at a rehabilitation center on Biscayne Bay that offers art, yoga and psychodrama courses--but no tennis.

A representative for Capriati confirmed Thursday that the 18-year-old tennis star entered an addiction treatment program at Mount Sinai Medical Center in Miami Beach.

“She’s optimistic. She’s very cooperative with respect to the program she’s in,” Capriati’s attorney, John Ross, told television station WPLG.

“I’m hopeful and fairly confident that Jennifer will come through this, that her judgment will improve. If my predictions are correct, whatever Jennifer decides to do, she will be a champion at it. She’s a good kid.”

For the first time, a Capriati spokesman challenged allegations that she used heroin and crack cocaine during a two-day motel room party preceding her arrest Monday for misdemeanor marijuana possession.

“This is coming from a crack head,” Ross said of the allegations. “Examine the source and make a responsible decision as to whether or not you think it’s credible.”

One of the two people arrested with Capriati, a 20-year-old drifter named Tom Wineland, alleged in an interview that she used crack during the party. Wineland’s attorney said he was told she was “whacked out on heroin.”

Police said they had no evidence Capriati used heroin or cocaine.

Capriati’s arrest prompted the cancellation of her multimillion-dollar endorsement contracts with Prince tennis racket company and Diadora, the Italian sportswear company. In Italy, an official for Diadora said the drug charge “offends the image” his company was seeking.

Capriati’s agent, Barbara Perry, flew to South Florida to join her client’s family. Capriati’s parents have visited her at the hospital, Perry said.

“They’re very much together and behind their daughter,” Perry said. “Under the circumstances I think they’re doing very well. They’re very strong. They’ve been through a lot.”