Carmen Cedeno left her daughter Lillian's bedside for only a moment. Two young doctors had entered the room to give the young cancer patient an injection. "Lilly smiled and said, 'Mami, you can go outside, this isn't going to hurt,' " her mother recalled.

Minutes later, the pregnant 21-year-old became the victim of an error that left her paralyzed and on the verge of death. Two resident physicians misread the label of a medicine, injecting into her spine a drug meant to be fed into a vein.

For a close-knit Puerto Rican family living on welfare in Schenectady, that day -- Feb. 27 -- was the beginning of a nightmare that has yet to end.

In her kitchen, Carmen Cedeno, a large, sad-eyed woman, sat in a house dress, weeping uncontrollably. Nearby, her husband, Anibal, an unemployed factory worker, held his head in his hands, dazed, barely able to speak. From the bedrooms of their apartment, where several of their eight children comforted each other, sobs emerged.

In the intensive-care unit of the huge red brick Albany Medical Center, 10 miles away, doctors struggled to keep Lillian Cedeno's 25-week-old fetus alive, even as life slipped from the mother's paralyzed body. Hospital administrators, who had released details of the incident Friday after media inquiries, refused to answer questions today. Guards patrolled the corridors of the hospital with walkie-talkies. A reporter was immediately ordered off the premises after talking with a nurse in the cafeteria.

"We have said all we are going to say," said spokesman Richard Ridgway.

Several weeks ago, the medical center had become the focus of national attention when Nathan Pritikin, the renowned author of health books, slashed his wrists and bled to death in the same room in which the Cedeno incident occurred.

In the ramshackle two-family house on Summit Avenue, where the Cedenos have lived since they moved here from Puerto Rico in 1982, there is no talk of anger, revenge or lawsuits. "We have faith in the Lord," said Carmen Cedeno.

Mrs. Cedeno, who recounted her story in Spanish because she speaks little English, said she had stayed by Lillian's bedside the night before the accident and had remained there on Feb. 27. "Lilly was in a good mood," Mrs. Cedeno said. "She was a bit sad, but she was joking, too. She was laughing. She was looking out the window."

About 6:30 p.m. two doctors entered the room. Mrs. Cedeno went outside, but Lillian's fiance, Francisco Valerio, stayed in the room while Lillian was given the injection.

"There were these screams and screams," recalled Mrs. Cedeno. Valerio stumbled out in a cold sweat, wide-eyed, panicked and sick to his stomach, she said.

About five minutes later, a nurse came to sedate Lillian with a shot and she quieted, Mrs. Cedeno said. "I was not alarmed. I sat down to have a cup of coffee, but about 20 minutes later, four doctors suddenly arrived with some nurses. They were very agitated. They said they had made a mistake. They had to remove the liquid from her spinal column."

Coincidentally, she said, Miguel Suarez, pastor of the family's Pentacostal Church, arrived to pay a visit. In an interview today, Suarez confirmed Mrs. Cedeno's account.

However, hospital spokesmen Friday said the error went undetected by the hospital for about an hour after a senior resident injected vincristine, a common anticancer drug, into Lillian's spinal column while another resident observed the procedure. The mistake was noticed by a nurse who went to prepare the patient for an intravenous injection and found a syringe missing, they said.

It was supposed to be Lillian's first scheduled chemotherapy treatment, which was to include three drugs injected intravenously and three into the spine, the spokesman said. Lillian had entered the hospital in mid-February for treatment of a malignant tumor in her sinuses.

Hospital spokesmen today refused to answer questions about the hours or shifts that the two residents had worked that week. Residents, who are in their final years of training, frequently work grueling hours and repeated night shifts.

The New York State health department is investigating the incident.

At the Cedeno home this morning, Anibal, red-eyed, said he had spent three hours at the hospital the night before but had not been allowed to see his daughter.

He brought his family to Schenectady, he said, because his 14-year-old daughter and 16-year-old son are retarded and he could not afford to send them to special schools in Puerto Rico.

He said he had worked on an assembly line at a Westinghouse Electronics plant in Puerto Rico. He had worked earlier in factories in Jersey City, N.J., he said. Here, he has yet to find a job.

Lillian is the third of their eight children. A recent color photograph, framed on the wall, shows a lovely young woman with short curly hair and a dazzling smile. "She was joyful," her mother said. "She was a gentle person. She was a homebody who didn't like parties and dances."

Asked if they are considering hiring a lawyer, the Cedenos looked confused. "We are thinking about Lilly, only about Lilly," Carmen Cedeno said.

In the living room a local television reporter is taping two of Lillian's sisters. A former brother-in-law, Floy Rivera, 28, on a visit from Brooklyn, is translating. Three- and four-year-old children scamper about, seemingly oblivious to the crisis.

In broken English, the sisters try to express their anguish. The television reporter questions insistently, "Do you miss her?"

Suddenly, Rivera explodes in angry tears, "Do we miss her! Do we miss her!" he cries. "You asked this! And especially when she has an unborn child? Her first?"

The television reporter signals her cameraman to switch off the klieg lights and put away the video camera. "I'm sorry," she said.