A federal appeals court, rebuking an Alexandria judge for what it called "glaringly" improper courtroom decisions, yesterday ordered a new trial for a couple who contended their daughter was left severely retarded after her spinal meningitis was misdiagnosed at a Quantico Marine Base hospital.

The 4th U.S. Circuit Court of Appeals, citing "disparaging" and "improper" comments and pro-government bias by District Judge Oren R. Lewis, also ordered that the new trial be held before a different judge.

The decision, by a three-judge appellate panel in Richmond, said Lewis "prevented effective cross-examination of the most important defense witness." It added, "All of the findings in the court's memorandum opinion . . . were virtually lifted verbatim from a report" by the government witness.

The panel also criticized comments by Lewis that a verdict in favor of the plaintiffs might raise the cost of malpractice insurance and that taxpayers would have to bear the cost of any damage award -- issues the appeals court said were irrelevant to the case.

William O. Snead III, the lawyer representing the couple, Scott and Linda Crandell, and their daughter Jennifer, 6, said yesterday that he and his clients were "thrilled" by news of the appeals ruling. The Crandells, both former Marine sergeants, live in Frederick, Md.

The couple's allegations of medical malpractice were dismissed last March after a three-day trial in Alexandria that was presided over by Lewis, 80, a semi-retired jurist with a reputation for outspoken courtroom behavior.

Lewis was criticized two months ago by the same appeals court, which upheld the bribery conspiracy conviction of former George Washington University professor Murdock Head despite what it called "distressingly frequent" trial interruptions by the crusty, white-haired judge.

The appeal filed by the Crandells said Linda Crandell took her daughter to the Quantico hospital on June 26, 1977, a Sunday, after she heard "strange sounds" coming from Jennifer's crib. The child, then 6 months old, was blue around the mouth, jerking her arms and legs and breathing with difficulty.

A physician's assistant who saw Jennifer that day diagnosed the symptoms -- including a fever of 104 degrees -- as a respiratory infection or a cold, recommended Tylenol and sent the Crandells home, the plaintiffs' appeal said.

During a visit two days later to the Quantico hospital, a physician told Linda Crandell that Jennifer was suffering from an ear infection.

On a third visit, on July 1, a second doctor diagnosed meningitis. Linda Crandell drove her daughter the same day to Walter Reed Army Medical Center in the District, where the diagnosis was confirmed.

Linda Crandell said yesterday that Jennifer remains severely retarded and in need of constant care. Experts testified on behalf of the Crandells that the daughter's retardation resulted from the failure to quickly diagnose the meningitis. Snead, the Crandells' lawyer, estimated that a lifetime of special training and care will cost more than $1 million.

Shortly before the 1981 trial, government lawyers suggested that another illness, infantile hypothyroidism, was the cause of Jennifer's retardation. An attempt by the Crandells to include that possibility--which they said they did not believe--in their lawsuit was denied by Lewis.

In the appeal, Snead maintained that Lewis exhibited not only pro-government bias, but confusion about the facts of the case.

"Now, I wanted more evidence and I didn't get it of whether or not the standard of care requires that a doctor give a spinal tap [a test for meningitis] to every infant that is sick or has a cold," the appeal quoted Lewis as saying. ". . . I can see that medical malpractice insurance if every time you've got a cold you tap to see if they have spinal meningitis."

Snead, who said he was arguing only that infants with Jennifer Crandell's symptoms should receive spinal taps, told the appeals court he found Lewis' statements "disturbing."