Although the condition of four of the five surviving Frustaci septuplets was reported as having improved today, medical officials remained cautious about their chances.

"They are all progressing as expected, considering their size and age," said Dr. Carrie Worcester, director of the Neonatal Intensive Care Unit at Children's Hospital. None of the babies was in immediate danger, she added.

"Their prognosis is critically stable, and I do not expect any of the babies to expire in the next 24 to 48 hours," Worcester told reporters. "Of course, no one knows . . . . You could have a disaster. But I would not expect any problem in the next 48 hours."

Officials said the major problem for all five babies remains severe hyaline membrane disease, which causes their immature lungs to inflate and deflate improperly. As of this afternoon, the disease was expected to reach its peak within 48 hours.

The infants also suffer from heart difficulties and jaundice. But these are considered neither surprising for premature babies nor especially life threatening.

Worcester said she was guardedly optimistic about the infants' prognosis, although she would not speculate on the odds of their survival. In previous meetings with reporters, officials said the babies have a 50-50 chance of surviving.

Ultrasound brain scan tests have uncovered no bleeding or other problems. Those results led medical officials to express guarded optimism today.

Worchester said the five infants, three boys and two girls designated alphabetically in order of birth, remain in critical but stable condition. Only the Baby B, a boy, failed to show improvement today.

Babies B and D had been described Friday as the sickest of the surviving five. But, Worcester described Baby D's improvement today as "100 percent."

Their mother, Patricia Frustaci, a schoolteacher who had taken a fertility drug, was described as upset over the death Friday of Baby F, a boy nicknamed "Peanut." He was the smallest of the six septuplets who were born alive.

Patti Frustaci, who is hospitalized at the adjacent St. Joseph Hospital, was "doing better" but remained physically exhausted, according to nursing supervisor Tes Payne. She is expected to remain hospitalized at least through the weekend.

Meanwhile, the Los Angeles Times reported that Samuel Frustaci, the infants' father, may have been too optimistic when he estimated that bills for the treatment of his wife and the surviving septuplets would run to about $700,000.

Hospital physicians, parents who have experienced multiple births and other experts said that the birth of the septuplets will probably cost at least $1 million.