Religious leaders generally have offered their nervous blessings to the medical technology which this week produced the world's first test-tube baby. They look with varying degrees of caution on where future developments in this field may lead.

Laboratory fertilization to produce human life is seen by many as a process that could aid couples who could not otherwise have children. While theologians expressed different views on the morality of the process, most Protestants and Jews and some Catholics favored the use of the technique. Many traditional Catholics condemned it.

"If nature played a trick, as it has in this case, if we can outsmart nature, that is theologically permissible," said Rabbi Seymour Siegal.

Lesley Brown, the mother of the laboratory baby, could not have a child because her fallopian tubes were blocked. Her doctor surgically removed eggs from her ovaries, mixed them with her husband's sperm, allowed the cultures to grow, and then inserted one into her womb.

A contrasting view was offered by Rev. Thomas C. Kelly, general secretary of the National Conference of Catholic Bishops.

"The fact that science now has the ability to alter this [process] does not mean that, morally speaking, it has the right to do so," he said.

The issue of whether it is permissible to assist conception in this way has also raised other far-reaching questions for religious leaders.

Some of the questions theologians as well as medical researchers and others are struggling with are these:

Has enough animal experimentation had been done to assure maximum safety in the process?

Is the process a form of genetic manipulation?

Does the process involve destruction of human life?

This last question is a particularly serious one for Catholic theologians.

In the laboratory methods of creating human life, a number of ripe ova are taken from the mother and mixed with sperm. Then, only the most promising culture is inserted into the womb and the rejects are destroyed.

"One can understand why, for the purpose of maximum efficiency, multiple ova are fertilized simultaneously," said Dr. Leroy Walters, director of the Kennedy Institute Center for Human Reproduction and Bioethics.

"For one who takes the view that life begins at fertilization, this leads to very serious questions," he said.

Dr. Walters himself does not take that view.

"Given what I consider the important good on the other side, namely the possibility of an infertile couple to have children of their own, I would say this good outweighs the eveil," he said.

Many traditional Catholics who are opposed to abortion are more troubled by what happens to the "discards," as Rev. Richard McCormick, also of the Kennedy Institute calls them.

"Is this an abortion? Is there human life present at this stage? There are reasons for doubting that we have a human being [at this stage], but I am not all that clear," he said. "I want to raise that question as vigorously as I can."

The safety of the process concerns many religious leaders.

"You have no right to use the process until you have the assurance that it is as safe as normal reproduction," said the Rev. Charles Curran of Catholic University.

Curran and other churchmen expressed doubt that there has been sufficient experimentation on animals before the process was tried on humans.

"It would be a terrible thing" if a mother impregnated through the laboratory process "should give birth to a badly-deformed baby, whose abnormality was due to something in the process," the Rev. Dr. Roger Shinn of Union Theological Seminary in New York said.

Dr. Shinn took a generally favorable view of laboratory fertilization but raised the specter of the use of surrogates to carry fetuses for women who would prefer to avoid going through pregnancy.

"I would find it offensive that a woman who wants children of her own but who didn't want to interrupt her career or who didn't want to lose her girlish figure - there could be a hundred reasons - could employ somebody to have the baby for her, in effect rent her body."

The medical developments which led to the birth this week of the world's first child conceived outside the womb came as no surprise to the theological community. Conferences and symposia dealing with the morality of emerging medical break-throughs, and involving the best minds from both theology and medicine, have been taking place for nearly a decade.

Physiologist Robert Edwards, who with British gynecologist Patrick Steptoe, was responsible for the Brown infant, has been a regular participant in such conferences.

Dr. Shinn, who came to know Dr. Edwards through these meetings, described him as "the kind of guy I really believe would not do it unless they have taken the precautions."

The Rev. Paul Ramsey of Princeton University has emerged as the most serious Protestant critic of the new technology.

In addition to joining in the criticisms of others he has also voiced fears that laboratory fertilization is the first step toward genetic engineering.

"That argument is an argument against doing anything for the first time," answers the Rev. Dr. John Fletcher, who is a clinical assistant of bioethics at the National Institute of Health.

"Because of technology and advances in knowledge, we are dealing with issues so often in the modern world in which there are no moral religious or legal precedents," observed Dr. Shinn. He added "these are ethical decisions that the human race never made before."