ENVER, Feb. 20 — The deaths over the last two years of three Colorado children whose parents denied them medical treatment on religious grounds has fueled support for state legislation that would prevent parents from using their religion as a defense against prosecution.

The parents of all three children belong to the General Assembly and Church of the First Born, a small denomination that believes in prayer, rather than medical treatment, to cure illnesses and disabilities.

Largely as a result of intense lobbying by the Church of Christ, Scientist, which also favors prayer over medicine, Colorado and 45 other states have statutes that allow parents to use their religious beliefs as a defense against prosecution for withholding medical treatment from their children. The exceptions are Hawaii, Massachusetts, Nebraska and North Carolina.

But with evidence that dozens of other children of parents with similar beliefs may have died in the last 25 years in Colorado, this state has become one of the first to consider eliminating the religious exemption, which its opponents say sanctifies a form of child abuse. The effort has rekindled a debate here, pitting religious freedom against the rights of children.

"I don't think freedom of religion should allow a child to die for not getting proper medical care," said State Senator Bob Hagedorn, a Democrat who is leading support in the Senate for a bill now under review in the House.

The United States Supreme Court has ruled that parents do not have an absolute right to deny their children medical treatment on religious grounds, saying in a 1944 decision that while parents "may be free to become martyrs themselves," "it does not follow they are free, in identical circumstances, to make martyrs of their children." The court reprised the same thought in a 1990 case.

But legal experts say that state and local officials have not seen the Supreme Court language as a clear directive for prosecution of child abuse and homicide cases. Congress did little to clarify the issue with a 1974 directive that required states receiving federal money for child abuse and prevention programs to have an exemption for parents who substitute spiritual healing for medical care. The requirement was rescinded nine years later, but by then, most states had enacted their religious exceptions, which effectively allow parents to treat ailing children through prayer without fear of prosecution if something goes wrong.

Then in 1996, Congress seemed to reverse itself in the Child Abuse Prevention and Treatment Act, saying there was no federal requirement that a child must be provided "any medical service or treatment against the religious beliefs of the parent or legal guardian."

In Colorado, for example, prosecutors have always been able to bring civil charges against parents who deny their children medical help under state civil laws. But few have, said State Representative Kay L. Alexander, the House Republican sponsoring the measure, which was approved 8 to 3 by the Criminal Justice Committee. Ms. Alexander said the exemption in the criminal code "has had a chilling effect" on local district attorneys.

Leaders from many of the dozens of churches that favor prayer over treatment say they have ample proof their spiritual healing works as effectively as a visit to a doctor.

Marvin Peterson, an elder of the church to which the families of the three dead children belong, said a member recently fell off a ladder and cracked open her skull. After elders prayed and anointed her with oil, he said, she recovered.

"I've seen people healed of cancer, seen it with my own eyes," Mr. Peterson said, taking strong exception to critics who characterize the church as a cult. "We believe that if it's the Lord's will, you will rise up."

While few critics of Mr. Peterson's church and other like-minded denominations argue with the right of parents to choose the manner of treatment for themselves, they assert that children have constitutional guarantees to medical care.

For years, Rita Swan has been one of the leading voices on their behalf as founder of Children's Health Care Is a Legal Duty, an organization based in Sioux City, Iowa, that lobbies for removing the state exemptions. Once a Christian Scientist, Mrs. Swan said that in 1977 a church "practitioner" — a member who is paid to pray — told her and her husband after several weeks of prayer that their 17-month-old son, Matthew, was suffering from a broken bone. Since Christian Scientists are allowed to consult doctors for broken bones, the Swans took Matthew to a hospital, only to learn he was suffering from spinal meningitis. He died a week later.

Mrs. Swan and Dr. Seth M. Asser, a pediatrician in San Diego, released a study in 1998 that found 172 cases of children dying between 1975 and 1995, more than 30 of them in Colorado, after their parents failed to get them medical treatment on religious grounds.

Mr. Peterson responded, "Children also die in hospitals every day."

Prosecutors have been loath to bring charges in many cases because of the ambiguities of the law and what they say are well-intentioned actions of parents whose religious beliefs are so strong that they prefer to put their children in the hands of God, rather than a doctor.

Frank Daniel, the Mesa County district attorney, had jurisdiction in the cases of the three Colorado children who died. He won a conviction for criminally negligent child abuse, a felony, in 1999 against the parents of an 18-day-old infant who died of meningitis. He declined to prosecute the parents of a 3-day-old infant who died of a heart defect. He said today that he had yet decided what to do in the latest case, involving Amanda Bates, a 13-year-old girl who died of complications of diabetes two weeks ago.

The county coroner, Robert Kurtzman, ruled her death a homicide.