The world's first test-tube baby - a child conceived in the laboratory, outside its mother's body - could be born in England in two or three weeks, the doctor who plans to bring it into the world said yesterday.

A mother identified only as "Mrs. A." is scheduled to give birth to the baby by Caesarean section in a government-funded National Health Service hospital at Oldham, 190 miles northwest of London.

The child she is carrying is a product of her own ovum or egg cell and her husband's sperm, joined in a laboratory apparatus because of a defect in her fallopian tubes, which ordinarily carry a fertilized egg cell to the womb.

After four days, the fertilized egg, which by that point had grown into a complicated aggregate of nearly a hundred cells, was transferred to her own womb for what her doctor hopes has been normal growth.

A successful birth would cap a dozen painstaking years of efforts by her doctor, 65-year-old gynecologist Patrick Steptoe. Since the 1960s, the well-regarded Steptoe has worked on this effort with Dr. Robert Edwards, 52, a Cambridge University physiologist.

The birth, and even yesterday's news, are also sure to arouse new debate about man's manipulation of nature. Many persons have asked whether humans are justified in taking a first step toward what might be a future test-tube race.

Steptoe's answer - stated in more or less the same words many times as he has lectured to medical societies on his research - is a simple: "All I want to do is to help mothers whose childbearing mechanism is slightly faulty."

The expected birth has already set off what threatens to become a media circus in Britain, however.

The first disclosure of the impending birth was made in a three-page story in London's Daily Express, which evidently broke the story after its competitor, the Daily Mail, bought up rights from the future parents for a reputed 300,000 pounds - $570,000.

The Daily Mail's purchase, said still another British newspaper, The Guardian, of Manchester, was made after "teams of reporters from many parts of the world" had bid on the story in what an unnamed health authority called "a gigantic international auction."

In a statement issued through the Daily Mail, which promised future "appropriate announcements" on its syndicated child, Steptoe complained about the "regrettable" lapse by the Daily Express in disclosing the story.

He said "it must be recognized that in the weeks ahead an atmosphere of total calm is vital" to the mother's and the child-to-be's well being.

However, he said any future announcements will be made through the Mail's syndicate, and he said he and Edwards had themselves urged the parents to make such a deal to relieve reporters' pressure on them and "to secure a financial future" for the child.

Sounding disgruntled, the Guardian complained that the monetary arrangement threatened "to produce the very reverse of the privacy and calm which doctors profess to want for the birth."

Among world scientists, however, the concern was more basic. A key question is: can such a child be normal?

Over the years, Steptoe and Edwards reportedly were on several occasions able to fertilize female eggs with male sperm in their laboratory.

Some clusters of new cells were then implanted in would-be mothers, but in no case did the pregnancy continue for the full nine months or, it is believed, anywhere near it.

The body, say medical scientists, usually expels organisms that should not be born. One American scientist has contended that "we must be very sure we are able to produce normal young by this method in monkeys" - close in physiology to human beings. - "before we have the temerity to move ahead in the human."

All the Steptoe-Edwards preliminaries are not yet known. But some scientists have transplanted test-tube mouse embryos into female mice, which then gave birth to what seemed to be normal litters.

Mrs. A., it was explained yesterday, became pregnant by the same method after nine childless years of marriage. Said to be 32, she and her husband, a railroad man in his late 30s, saw consultant after consultant about her failure to conceive and were finally directed to Steptoe.

Steptoe's test-tube technique is not the same as cloning, which would create a child from a single cell of just one parent, with the aim of producing a duplicate of that parent. The recent book, "In His Image," in which writer David Rorvik claimed to report a successful cloning, has been attacked by scientists as a hoax.

Steptoe's ethics were endorsed in a special session last week of the central ethical committee of the British Medical Association, it was also learned yesterday. Dr. John Lawson, the committee's secretary, said, "Used responsibly, the (Steptoe) technique offers no ethical difficulties for doctors" and could be a "a valuable addition to the treatment of infertile women."

Steptoe did not explain yesterday why he plans to deliver the baby by Caesarean. One American doctor speculated that he may have been influenced in some way by his previous experience in incomplete test-tube pregnacies.

Three years ago another British gynecologist, the then well-regarded Prof. Douglas Bevis of Leeds University, said three test-tube babies were conceived in the laboratory and that he implanted them in mothers' wombs for three successful births - one in England and two in other countries.

He offered no further proof, and this and other such claims are believed groundless, David Sanders, spokesman for the British government's Medical Research Council, said yesterday.

As for Steptoe, he made his only fact that the news of the expected birth had come out at all, he said any misfortune arising from premature reporting "will be on the shoulders of ity. We therefore ask that the media leave both the hospital and our patient alive."