RIVERSIDE, CALIF., APRIL 29 -- After two months of investigation and three autopsies, local officials in this desert-edged suburb conceded today that they still have not solved the mystery of what caused the bizarre collapse of a half-dozen hospital workers caring for an emergency room patient.

The officials said they have concluded that the patient, 31-year-old Gloria Ramirez, died of heart and kidney failure caused by her cervical cancer that night in February and the case has been closed. But neither the Riverside County coroner's office nor the hospital could explain the workers' claim that the dead woman's blood emitted toxic, ammonia-like fumes that sickened them.

Ramirez's family responded today that an independent pathologist they hired, Richard Fukumoto of Orange County, reached a preliminary conclusion that she did not die of cancer. Her relatives angrily accused officials of bungling the investigation and concealing unsafe conditions at Riverside General Hospital, where the incident occurred.

"It takes them 10 weeks to say she died of natural causes?" asked Maggie Ramirez-Garcia, the dead woman's sister. "I don't believe anything the county officials or the coroner says." The family's pathologist has yet to receive tissue slides or blood tests from the coroner's office to assess the extent of the cancer.

County officials said their investigation exonerated conditions at the public hospital west of Los Angeles, the county's largest health and trauma center. Riverside General has a history of problems with ventilation in patient treatment areas, including the emergency room, according to state workplace safety records.

In April 1993, the California Occupational Safety and Health Administration notified Riverside General that the first-floor emergency room was permeated with "sewer gas" from a drain. The hospital also was cited in 1991 when two employees sought medical treatment after a possible leak of a hazardous gas from a sterilizer. In 1992, the hospital was notified that an inspection found algae growing in a water reservoir.

Thomas DeSantis, a county spokesman, acknowledged some previous ventilation problems but said the emergency room's vents were checked by several independent inspectors as a result of the Feb. 19 incident and the hospital was given a "clean bill of health."

The Ramirez family contends the hospital has portrayed Gloria Ramirez as a "toxic monster" to conceal its own possible culpability in her death. "I honestly believe my sister may have lived if she hadn't gone into that emergency room that night," said Ramirez-Garcia. "I don't know what {the county} is afraid of, but we want answers."

A noted forensic pathologist not involved in this case commented that the hospital's original version of events was "very interesting and very misguided."

"There's no way fumes can come out of a body and hurt people. That idea went out with the Dark Ages," said Michael Baden, former chief medical examiner for New York City, in a telephone interview. "This kind of thing gives death a bad name. Dead bodies don't make people sick."

The investigation into Ramirez's death was troubled from the beginning. A top-level investigator in the county coroner's office who was in charge of the Ramirez case committed suicide a month into the probe. The official, Stephanie Albright, "may have been under pressure" from the case, said deputy coroner Dan Cupido.

Last week the county announced that a key piece of evidence -- the syringe used to draw Ramirez's blood in the emergency room -- had been inadvertently discarded.

An unemployed mother of two children, Gloria Ramirez had been undergoing treatment for cervical cancer for six weeks when she complained of nausea and began vomiting on Feb. 19.

Maggie Ramirez-Garcia said she believed her sister had begun chemotherapy or radiation treatment the week she died. The cancer was advanced, Ramirez-Garcia said, but was not supposed to be fatal.

Ramirez's boyfriend, Johnnie Estrada, said he called for an ambulance about 8 p.m. because she was having trouble breathing. At the hospital a few minutes later, the bizarre sequence of events began. A nurse who began drawing blood noticed an ammonia smell and fainted. A doctor, a third-year resident, who took over for the nurse, drew the syringe with Ramirez's blood close to her nose, breathed in and fainted too.

Some other members of the medical team also grew faint, although others did not. The doctor and nurses who became ill later said they saw crystals in Ramirez's blood, but others neither saw the crystals nor smelled the odor.

A doctor ordered the emergency room evacuated. Ramirez, who the hospital maintains remained under constant care, died at 8:50 p.m. Her body was placed in a separate room and later sealed in double-plastic bags and an airtight steel container.

The first autopsy, which took place six days after Ramirez's death, was conducted in an airtight cubicle with pathologists wearing protective suits provided by the county's Hazardous Material squad.

The second examination came a month later. The third, demanded and paid for by the family, came only after the county released the body under court order. The county finally relinquished the remains for burial last week after it said in court that its searches of Ramirez's remains produced nothing that could be called a public health hazard.

Although county officials insisted they had done the best possible job, a news conference held today at the county administrative building suggested ongoing conflicts between health officials and the coroner's office. The health officials came on first, relating their findings that the hospital facilities were operating "safely and effectively" before, during and after Ramirez's death. Then, after fielding a handful of reporters' questions, they left the room.

Coroner Scotty Hill and deputy coroner Cupido came on next, attempting to restrict their comments to the reasons for Ramirez's death.

Cupido stressed that she died from natural causes. He had said after the initial autopsy that Ramirez died from other than natural causes. Today he could not explain the conflicting statements. He also could not explain the odor described by the workers but said "no external toxic substance" was found in Ramirez. Neither group was prepared to offer a conclusion about why the hospital workers collapsed that night, but when county spokesman DeSantis was asked if the county would continue its investigation, he responded: "It's finished."