A British gynecologist and this city's sensationalist tabloids have turned the expected birth of a baby conceived in a laboratory into one of the wildest commercial circuses ever staged in Fleet Street.

The Daily Mail, which outbid the U.S. National Enquirer and publisher Rupert Murdoch, has paid an estimated $560,000 for "exclusive world rights" to stories and pictures of the fetus. But some of the Mail's chief rivals in the cheesecake-shock-gossip derby here have already been depreciating the asset with scoops of their own.

The gynegologist, Dr. Patrick Steptoe, who says he has developed a technique to conceive a baby outside the womb, has already acknowledge a role in the event's commercial exploitation. Tuesday, he ticked off the prospects.

"There are rights for newspapers in Britain and separate rights abroad," he said. "There are TV, radio and book rights. The whole thing is enormous - but first we have to produce a normal, healthy baby."

That baby will be the product of the mother's own egg cell and her husband's sperm, joined in a laboratory apparatus because of a defect in the mother's fallopian tubes, which ordinarily carry a fertized egg cell to the womb. Four days later, the fertilized egg was transferred to the mother's womb.

"Because of the unique nature of this forthcoming birth, there is enormous public interest," Steptoe said. "We have therefore advised the parents that the wisest course was to make a special arrangement with an international agency."

That agency is the syndicate arm of Associated Newspapers, publishers of the Mail. Yesterday, the paper's managing director, Alwyn Robinson, disclosed that Steptoe and his partner, Dr. Robert Edwards will themselves write first-person accounts of the affair, and that these will be sold as part of the Mail's package of articles and pictures.

Will Steptoe and Edwards be paid for their literary efforts?

"That's a fair assumption," Robinson said with a laugh. But the mail will not say how much the doctors will earn. Nor will it disclose the share going to Gilbert and Lesley Brown, the parents of the test-tube baby.

Although the Enquirer, one of America's more sensationist weeklies, could not match the Mail's bid, it did got American rights to the story for an undisclosed sum and will now sell them to any U.S. paper, radio or television station willing to pay.

Murdoch, the Australian magnate who recently added The New York Post and New York magazine to his chain of British and Australian papers, has already begun recouping for his failure to win the British bidding derby.

Murdoch's Sun, with its regular display of pictures of nude models, has become Britain's biggest selling paper. It carried an exclusive interview yesterday with the father of the test-tube baby. Gilbert Brown, a 38-year-old truck driver, was quoted as saying, "We don't want to make any money out of this - we just want our baby."

The Mail countered by splashing an interview on its front page with his 32-year-old wife, Lesley.

"This is a scientific miracle," she was reported to have said. "But in a way, Science has made us turn to God . . . We just had to pray to God to give our thanks."

But it is the Daily Express that won, the honors in Fleet Street, scooping the Mail on Tuesday on the Mail's own story. In boxcar type, the paper cried, "Baby of the Century."

The paper was still crowing yesterday. It trumpted: "Follow the Daily Express yarn of recent years, its announcement that Martin Bormann was alive and well in South America. That one is still exclusive, for Boarmann had been dead for 27 years. It cost the Daily Mail thousands." It boasted of other alleged scoops it had scored. Missing from the list, however his rival's sucess.

The editor of the Mail, David English, said he was not at all put out over his rival's success. "You couldn't really print an exclusive story on this. What we'll have is a great wealth of detail," he said.

So far, only one paper, The Guardian, has taken a dim view of the goings-on. It complained that authorities at the hospital where Lesley Brown is confined were channeling all press inquiries to the Daily Mail.

It noted that gynecologist Steptoe had issued a plea for "an atmosphere of total calm" only after the Express had broken the Mail's projected monopoly.

That plea, said a Guardian editorial, "would have been received more sympathetically if he himself had not been one of the main instigators of the checkbook deal."

Steptoe, however, refused to answer calls yesterday so the reply came from Robinson of the Mail.

The administrator at the Browns' hospital, Ed Warren, explained that authorities had turned all reporters over to the Mail because it was in "the best commercial interests" of his patient.

Last night, a spokesman for the British Department of Health said that the government forbids discriminating in favor one one newspaper against another. The British Medical Association had nothing but applause for Steptoe's conduct.

Dr. John Dawson, assistant secretary to the association, said:

"In general terms, it is a doctor's job to act responsibly, in the best interests of his patient. Speaking personally, from what I have read and heard, Mr. Steptoe has acted entirely in the interests of his patient. Making provision for the child might well be in its best interest."

The Browns, however, do not appear to be hard-pressed. In fact Gilbert Brown makes $113 a week while his wife had been earning about half that in a factory. Together the pair earn more than the average family [TEXT OMITTED FROM SOURCES]