BOCA RATON, Fla. - Jennifer Capriati checked into a drug and alcohol rehabilitation center amid allegations she used heroin, crack cocaine, alcohol and painkillers during a two-day party, a spokeswoman for her management agency said today.

Capriati voluntarily entered the rehab center at Mount Sinai Medical Center in Miami Beach yesterday, two days after her arrest at a Coral Gables motel for possession of marijuana. Two companions who pulled up in her car during a police search of her room were arrested for possession of heroin and cocaine.

A spokeswoman for International Management Group, speaking on condition that she not be identified by name, told The Associated Press that Capriati, 18, had entered Mount Sinai.

Barbara Perry, also of IMG, told USA Today that Capriati's parents had visited her in rehab and that "everything's fine; she's in good spirits."

Smoking a cigarette, her face and body bloated, Capriati recently tried to cash a check for $300 at a supermarket in Boca Raton. Carrying no identification, the multimillionaire teenage tennis star was turned down.

"The manager came up to me and said I never would have recognized her," said former player Carling Bassett Seguso, who shops in the same store in this posh tennis and golf mecca.

Bassett Seguso told the story yesterday with sadness and a sense that she could see Capriati's troubles coming.

One of the two people arrested with Capriati, 20-year-old Tom

Wineland, alleged in an interview that she used crack cocaine and a dangerous combination of painkillers and alcohol during a two-day drug spree over the weekend.

Wineland's attorney said he was told that Capriati was "whacked out on heroin" during the party at her motel room in Coral Gables.

"To me, she's going through what entertainers sometimes go through," Bassett Seguso said. "She has that type of personality. . . . When she was playing tennis, she went through that whole thing - black nail polish, all those things in her ears. It's probably a blessing in disguise she got caught."

Capriati paid for the drugs last weekend with cash advances from her credit cards, and the others arrested with her went out to buy them because she was too high to go along, said Edward Abramson, attorney for Wineland.

In Italy today, an official for Diadora, the Italian sportswear company, said it ended its multimillion-dollar endorsement deal with Capriati.

The drug charge "offends the image" Diadora was seeking, Evan Nonni said.

The New York Times reported today that Prince tennis-racket company has canceled its contract with Capriati.