A judge said Monday that shipping heiress Christina Onassis apparently died of natural causes, but he refused to rule out the effects of drugs.

Judge Juan Carlos Cardinali told United Press International that he has gotten a verbal report from medical examiners who concluded they "found nothing that would indicate the cause of death was from other than natural causes.""I do not have the definitive result (of the autopsy)," the judge said. "I also cannot rule out (the role) of some chemical element, such as barbituates or amphetamines."

Toxicologists are reported to have examined a bottle of pills, the contents have not yet been divulged, found beside the Onassis body after she died Saturday morning.

The Onassis family has said the 37-year-old heir to the shipping fortune of the late Aristotle Onassis died of a heart attack in the vacation home bathroom of Marina Dodero, wife of the administrator of her estate.

But Judge Alberto Daniel Piotti said Monday that he would not authorize return of the body to Greece "until there was conclusive proof that the death was the result of natural causes."

A report on an autopsy done late Saturday was in a sealed envelope under the jurisdiction of the Buenos Aires medical examiner's office.

In Athens, Ioannis Georgakis, vice-chairman of the Alexander Onassis Foundation, said Onassis' body was expected to arrive on the Greek island of Skorpios Thursday or Friday and would be buried in a family plot beside her father and brother.

He said the 37-year-old daughter of the late magnate Aristotle Onassis "had no health problems," and he rejected speculation that she committed suicide.

"She died of heart failure," he said.

Relatives and business associates of the family attended services Sunday for Onassis at a chapel at the headquarters of the Buenos Aires branch of the Greek Orthodox Church.

A cousin of Onassis, Annabella Onassis, told Argentine reporters Saturday night that Christina "died in the bathroom of the home of the Dodero family. She did not have health problems."

She said Onassis attended a country club party Friday night and appeared to be well.