The world's first human pregnancy from a fertilized egg that had been frozen, thawed and implanted in the mother's womb is stirring intense controversy in Australia, raising ethical and legal questions along with some demands to end this aspect of the "test tube baby" program.

The questions range from the fundamental to the relatively picayune, from the issue of defining the human being to the problem of who gets custody of the frozen egg if the prospective parents separate.

Some of the sharpest criticism of the program came from Margaret Tighe, the president of the Right to Life Association in the state of Victoria, where an unidentified Australian woman is entering her fourth month of pregnancy with an embryo that had been stored for four months before being thawed and implanted.

Though definitions vary, many scientists hold that the fertilized egg becomes an embryo as soon as it starts dividing. Within three days, it becomes a clump of eight cells, though it does not begin to show rudimentary division into human organs for two weeks.

Tighe said human embryos were being treated "with as much respect as frozen peas" and called on the state government to prohibit "this gross experimentation with human life."

Further criticism came when the medical team that achieved the feat disclosed that two of the eight cells of the frozen fertilized egg had been damaged by ice crystallization before being reimplanted.

"One can only hope that the 14-week unborn baby who has been the subject of this experimentation will be a normal child," said Alan Baker, the president of Pro-Life Victoria, after the pregnancy was announced two weeks ago.

He told The Australian newspaper that the successful pregnancy was achieved at the expense of 18 other normal embryos that were frozen, thawed and later died.

In vitro fertilization, which is used in women whose fallopian tubes are missing or blocked and who therefore cannot conceive, involves the removal of an egg from the woman's ovary and the union of the egg with the father's spern "in vitro"--in a glass dish. The fertilized egg is then implanted in the mother.

The debate about the Australian advance of in vitro fertilization, better known by its misnomer as the making of "test tube babies," began shortly after a medical team in Melbourne announced May 2 that it had successfully implanted a previously frozen and stored embryo in a human being for the first time. The announcement said the mother was 14 weeks pregnant with an apparently healthy fetus.

The team is prepared to implant more stored embryos in mothers who cannot conceive naturally. At least 35 other human embryos remain frozen in liquid nitrogen at Melbourne's Queen Victoria Medical Center.

Dr. LeRoy Walters, director of the Center for Bioethics at Georgetown University's Kennedy Institute of Ethics, said Monday he knows of no program in the United States in which embryos are frozen. Pointing out that "a good record of safety has developed" in the freezing and thawing of certain animal embryos, he added that "one simply doesn't know for sure what the safety record will be for human embryos."

The ability to freeze and store fertilized eggs can reduce the number of repeat steps in in vitro fertilization, where it is often necessary to make several implantations before pregnancy is achieved, U.S. researchers said after the Australian announcement.

Meanwhile, a week after the frozen fertilized egg announcement, doctors in Adelaide announced that a local woman was expecting the world's first test-tube triplets next month.

Since the first test tube baby was born in Britain in July 1978, about 150 children, including a set of twins, have been conceived though the process.

Nevertheless, the latest development in Melbourne caught Australians by surprise.

A senior judge of Australia's Family Court warned that the legal system was unprepared for many of the potential problems raised by in vitro fertilization, particularly frozen embryos. He said it now was legally possible for such embryos to be bought, sold and even destroyed.

He envisaged legal tangles on the "disposition of the embryo" if the parents of a frozen egg decided to separate. This might require courts to decide whether the embryo was "property," in which case the wishes of the legal owner would prevail, or a custody problem, meaning that the court could consider the welfare of the child.

Dr. Alan Trounson, scientific director of the program that froze the embryo, noted that women whose embryos had been stored could later become medically unfit for pregnancy. "What do we do" then? he asked, according to the Canberra Times newspaper. "We cannot force parents to have them."

The Australian raised other potential dilemmas editorially. "What happens if the embryo is damaged during the freezing or thawing?" it asked. "If a resulting child were deformed, could the child or its parents claim compensation, and from whom?"

A committee named by the Victoria state government to study ethical aspects of in vitro fertilization is expected to deal with frozen embryos.

In the United States, the Department of Health and Human Services bans federal funds for in vitro research and human use of the in vitro method. A 1978 report from the department's Ethics Advisory Board found such laboratory research and human use of the method ethically "acceptable." The department has not acted on this.

Roman Catholic reaction to in vitro fertilization is negative, said the Rev. Edward Bryce of the Office of Pro-Life Activities of the National Catholic Conference.

Rabbi Seymour Siegel, a professor of ethics and theology on leave from the Jewish Theological Seminary in New York, said Jews "are generally in favor of such procedures" because "it makes it possible for childless persons to have children." Main-line Protestant churches, still studying the issue, have not taken a stand against it, The Rev. Arleon Kelly, assistant general secretary of the National Council of Churches, said.