The British doctors who pioneered the technique that produced the world's first test-tube baby yesterday released the only details so far disclosed on their scientific breakthrough.

In a letter to The Lancet, a British medical journal, doctors Patrick Steptoe and Robert Edwards said the tiny egg that grew to become Louise Brown, the world's first "test-tube" baby, was kept in a glass bowl for two-and-a-half days.

The letter said two-and-a-half days after the egg was removed from Lesley Brown, the mother, for fertilization by her husband's sperm, an eight-cell embryo was implanted in her womb.

The doctors said the fetus had grown slowly for several weeks after the 30th week, but grew considerably during the last 10 days before being delivered by caesarian section.

They said the baby was delivered 38 weeks and five days after its mother's last menstrual period.

Brown, 31, gave birth to the six-pound baby girl in Oldham, England, 17 days ago.

International interest was drawn to the child's birth a month ago when the doctors announced that the event was imminent. At least part of the interest was rooted in the controversial purchase by The London Daily Mall of the full rights to the story for a sum reportedly in excess of $500,000.

Even routine medical bulletins thereafter were being given out through the newspaper until a top-level government decision eventually forced the hospital to give out at least basic medical information. Beyond that, however, information on the child and the technique that made her birth possible have been sketchy at best.

The doctors gave no details on one of the more difficult parts of the technique, preparing Brown with hormones so that her womb would not reject the embryo, as a body sometimes rejects a heart transplant.

Steptoe and Edwards said they hoped to publish further details at a later date, such as how they decided the best moment to implant the fertilized egg into Brown's womb.

The Steptoe-Edwards technique was used on Brown because of a blockage in her fallopian tubes, which transport the eggs from the ovary to the womb.