BOSTON -- David and Ginger Twitchell returned to their native East Coast from Los Angeles four years ago to build a quiet life with their two sons, Jeremy, 2, and Robyn, 6 months. Two years later, Robyn died of a bowel obstruction. And today, his death is under investigation by the Suffolk County district attorney for possible charges of neglect or manslaughter.

"There will be some people who will say we didn't care enough," David Twitchell, 32, said in a recent interview at the retirement home where he works. "But what is neglect? We used extreme measures to try and save Robyn . . . extreme Christian Science measures."

The Twitchells are one of five Christian Science families under legal challenge in the death of a child. The other four cases, three in California and one in Florida, already are in the state courts -- and in each, the parents contend they did everything they could do in good conscience to save their children, using a 100-year-old system of prayer called spiritual healing. They believe that their religious convictions, the First Amendment and state statutes allow them to forgo medicine for prayer.

In some respects, their cases resemble others in this decade in which lower courts generally have ruled that parents have no right to endanger a child's health when practicing their religion. The parents, who usually have received probationary sentences, have chosen not to prolong their ordeals -- or risk a definitive ruling against their position -- by appealing to the U.S. Supreme Court, according to legal experts.

But the Twitchell investigation in Boston, headquarters of the Mother Church to which all Christian Science congregations report, is unusually sensitive because a top official of Christian Science was told about Robyn's condition before the boy died.

A trial here would produce a high-level confrontation between modern medicine, whose methods and limits are under increasing scrutiny, and the faith of a church that enjoys a respect broader than its modest membership figures might suggest.

"T'ain't easy to decide which way to go," said District Attorney Newman Flanagan, who asked a District Court judge more than a year ago to consider the evidence. He recently received the judge's recommendations, which, like all other records in this case, have been sealed.

The Twitchell case goes beyond legal debate to reveal a clash of two cultures with long histories in this tradition-bound city. Christian Science, its modern 26-story administration building in posh Back Bay masking its Puritan roots, could find itself pitted against the scrappy Irish Catholic political establishment that helped put Flanagan in office.

The Irish, the largest voting bloc in this city of 574,000, have run it for most of the century. Since 1932, only one mayor of Boston has not been Irish. The current mayor, Raymond Flynn, is Irish. And many neighborhoods, including the one where the Twitchells moved, are almost exclusively Irish.

Flanagan, completing a third term as prosecutor in a 50-year-old courthouse where the elevators are still run by operators, is not one to pick a fight, those who know him say. But he does not shy away from one, either.

In 1974, he successfully prosecuted Kenneth Edelin, a Boston City Hospital physician, over the objections of blacks and feminist groups for performing an abortion illegally. Eight years later, he drew the wrath of whites for prosecuting five white men who chased a black man into a train tunnel to his death. In 1983-84, he served on the U.S. Attorney General's Task Force on Family Violence, which concluded that the abuse of children and others is a crime, not a matter of personal belief on how to handle children.

Flanagan acknowledges that Christian Science "is a religion that is well thought of." The church publishes an internationally respected newspaper, The Christian Science Monitor, owns a local television station, runs a daily radio broadcast and employs 1,500 people at its headquarters here. Mayor Flynn recently declared a First Church of Christ, Scientist Day to recognize church-sponsored projects for the elderly.

Such legitimacy is remarkable given the denomination's declining size and its almost mystical understanding of a relentlessly material world. Bylaws prohibit membership counts, but officials say there are fewer believers than the 269,000 last counted by the U.S. Census Bureau in 1936. The number of practitioners -- members trained in spiritual healing -- has dropped from 12,000 to about 3,000, they say. There are no preachers in its churches, and generally no traditional Christian sacraments such as weddings and communion.

One mark of the church's influence is that lawmakers in at least 44 states, including Massachusetts, have rewritten child-abuse laws to accommodate its views on spiritual healing.

Those accommodations, also called religious exemptions, contribute to the legal morass for parents and prosecutors. The Massachusetts child-abuse law, for example, says in part, "A child shall not be deemed to be neglected or lack proper physical care for the sole reason that he is being provided remedial treatment by spiritual means alone in accordance with the tenets and practice of a recognized church."

Another section stipulates: "Parents who fail to provide medical services to children on the basis of religious belief are expressly precluded from imposition of criminal liability."

Rikki Klieman, the Twitchells' attorney, believes the Twitchells "obeyed the law of Massachusetts . . . . To now criminalize them, when they had no notice of any wrongdoing, would be a complete constitutional deprivation."

Flanagan, however, could decide to interpret the abuse statute differently. He could argue that religious exemption denies children equal protection of the law in violation of the U.S. Constitution. He could decide that the state's homicide law should be applied in this case.

One of a very few Supreme Court cases that could guide him is a 1944 decision, Prince v. Mass., in which the plaintiff, a Jehovah's Witness, unsuccesfully challenged Massachusetts' right to restrain her use of children to distribute religious literature. The justices said "the right to practice religion freely does not include liberty to expose the . . . child to . . . ill health or death."

The Twitchells' attorneys play down the decision's importance, saying that it involved a challenge to an unrelated statute and that the potentially pertinent sections were written as guidance, not precedent.

Nothing in David Twitchell's Long Island childhood prepared him for this crisis. His father, a schoolteacher, and his mother, an artist, were Christian Scientists, but they did not rule out doctors' visits when their children were sick.

Although Twitchell won a New York state scholarship in biology, he chose political science as a major when he enrolled in Principia College in Elsah, Ill., the country's only Christian Science college.

There he met Ginger, who, according to David Twitchell, had had a rockier childhood growing up in Maine. Her mother, a devoted Christian Scientist, had died in childbirth with her sixth child when Ginger was relatively young. Her father, also a Christian Scientist, remarried. His wife did not share his faith. The children first lived with their father, then with grandparents.

Ginger Twitchell declined to be interviewed for this article. "This has been harder on {Ginger} than on me," her husband said.

After what David Twitchell described as "a long courtship," the couple married eight years ago. They decided that Ginger would work at home "so she could care for the children." David took a job as an assistant administrator in a Christian Science retirement home in Los Angeles.

Ginger gave birth first to Jeremy, then to Robyn. "Robyn had big brown eyes, just like his mother," Twitchell recalled. "He leaned toward her, just as our older boy leaned toward me . . . . He was always coming up and giving her a hug." Robyn was about a year old when the couple moved into the top floor of a two-family home here in Hyde Park, a middle-class neighborhood.

A Boston Globe account published after Robyn's death, before the sealing of court records, said that on April 4, 1986, Robyn grew "feverish and lethargic." The Twitchells called in a Christian Science nurse, who saw to his basic needs such as cleanliness, and a practitioner who led them in spiritual healing.

David Twitchell, citing a judge's instructions, would not describe what he and his wife did once Robyn grew ill. But church officials say that as Christian Scientists, the Twitchells would have assumed that Robyn's suffering was evidence that they had failed in their understanding of God. They would have been expected to renew their praying and their study of the Bible and the writings of founder Mary Baker Eddy. Medical intervention would have been discouraged because it would emphasize their son's body over his spirit.

The practitioner and the Twitchells contacted Nathan Talbot, top spokesman for the Mother Church and director of the church's Massachusetts Committee on Publication. Talbot said the church requires a practitioner to call his committee director in "serious child cases," to ensure that the practitioner has notified civil authorities of the illness when required by law, usually in the case of a communicable disease.

The Globe quoted Talbot as saying that he was told the boy was receiving appropriate Christian Science treatment, "deep Christian prayer."

According to the police account in the Globe, Robyn went into convulsions at 10 p.m. on April 8. He showed no signs of life when he arrived with his father by ambulance at Carney Hospital in nearby Dorchester at 11:10 p.m., according to a hospital spokeswoman. The emergency room crew administered cardio-pulmonary resuscitation for 17 minutes before a physician pronounced him dead at 11:27 p.m.

The county medical examiner attributed the boy's death to an obstructed bowel. In small children, the condition is sometimes the result of a congenital abnormality or trauma and sometimes unexplained, according to Dr. Edward Penn, Massachusetts chapter president of the pediatrics academy. Symptoms include vomiting, lack of bowel function and a swollen belly. The condition is "unusual, but not rare," Penn said, and is treated with an enema, antibiotics or surgery.

Medical treatment apparently would not have been out of the question for Robyn, given his father's history. "I've always been aware of all the alternatives," said Twitchell, who had dental surgery not long ago after praying for a year that his aching tooth would heal.

But prayer had to come first. Klieman, Twitchell's attorney, said Robyn experienced a period of apparent improvement. "The Twitchells had every reason to think their prayer was working," she said.

The Twitchells have made some changes in their lives since Robyn's death. They have moved to an undisclosed suburb, and they have had another baby, Brian, now 6 months old. If he were to get seriously ill, David Twitchell said, "we would consider all the options."

But a change of scenery does not eliminate the doubts or relieve the overwhelming sadness.

"It has been tough," Twitchell said. "Some people might call it a severe test of your faith."