WASHINGTON — A well-known Italian fertility specialist and his U.S. colleague have announced plans to clone human beings, apparently becoming the first scientists with expertise in human reproduction to publicly set such a goal.

They may well succeed, cloning experts said Saturday — but not without causing great damage.

Cloning would likely produce stillborn and diseased children, they said, and might provoke lawmakers to seek bans on a broad range of medical research, such as work that uses tissue from human embryos to try to cure disease. The two scientists stressed that their cloning procedure would be offered only to couples who cannot bear children by other means.

We are serious people and have a track record to show for it," said Panayiotis M. Zavos, professor of reproductive physiology at the University of Kentucky. "Cloning has already been developed in animals. The genie is out of the bottle. It's a matter of time when humans will apply it to themselves, and we think this is best initiated by us ... with ethical guidelines and quality standards."

Zavos said he is working with an Italian researcher, Dr. Severino Antinori, who has already pushed the boundaries of fertility treatment by helping women become pregnant well after menopause, including a 62-year-old woman.

The two men announced their plans Thursday at a conference in Lexington, Ky., and Zavos said Saturday that they had lined up 10 infertile patients who want to be cloned and 10 other researchers who want to help. He declined to name any. He said the work would be done in an undisclosed foreign country.

Cloning experts said the announcement signals that the technology has matured . They feared Zavos and Antinori might provoke a backlash against medical research by raising fears that scientists have crossed ethical boundaries.

The cloning plan "just invites prohibitions across the board that shuts down the very research we need to cure disease," said Ronald Green, a Dartmouth University bioethicist .

Equally worrisome to some researchers is that when cloning fails, it often fails in gruesome ways. For every successfully cloned cow, sheep or goat, dozens of others fail to grow in the womb, die at childbirth or perish soon after birth from deformities .

"As far as cloning a human being, it's definitely an achievable feat — unsafe and unethical, but achievable with the right resources and know-how," said Dr. Robert P. Lanza, vice president of scientific development of Advanced Cell Technology Inc. in Worcester, Mass., which has cloned cows and goats. "Cloning is conceptually very simple, so someone with the drive has a real chance of succeeding."

The problem, said Rudolph Jaenisch, a cloning expert at the Massachusetts Institute of Technology, is that "there will very likely be defects , and this is very irresponsible."

Cloning is a process for creating a genetic duplicate of an individual. Although the offspring may not look or behave exactly like the parent, it has the same genes. In the four years since the arrival of Dolly, the famous sheep and the first cloned mammal, scientists have successfully cloned cows, pigs, mice and other animals.

In cloning, scientists start with an egg cell. They remove the egg's DNA, then insert DNA or even a whole cell from an adult animal. It was a mammary cell from a 6-year-old ewe that produced Dolly, but skin and other adult cells have also been used.

When the process works, the egg cell begins dividing and grows into an embryo. The embryo is then transferred to a surrogate mother and grown to term, just as human "test-tube" babies are produced at fertility clinics.

Scientists believe that cloning often fails because the adult DNA retains some features of its former life as a mammary cell, skin cell or other type of cell. It took 277 attempts to clone Dolly, which produced only 29 embryos that could be transferred to a surrogate mother. A single one grew to term and was born as Dolly.

Zavos, in an interview Saturday, said he was well aware that many cloning efforts produce flawed embryos. But he said existing techniques, and those he and his team hope to develop soon, would give scientists the ability to determine which embryos will grow successfully and which are bound to fail.

Zavos, 56, said he has known Antinori for 15 years and began talking with him about the cloning project in 1988. Zavos is the president of ZDL Inc., a private corporation that markets infertility products. Government records show that Zavos has been granted four patents in the last decade on laboratory devices and techniques.

Antinori is the director of a Rome-based artificial insemination clinic. He attracted international attention when he treated a 62-year-old woman with hormones so she could conceive. She gave birth to a boy in July 1994.

The process of cloning human embryos for medical purposes could yield information that would help make it a viable technique for reproduction, specialists said.

"There are many teams in the world that are on this project, so I don't think Zavos is the only one," said Lanza. "There are groups in China, Europe, the United States, though very few who are thinking of using this to generate identical human beings. Most reputable scientists believe that is crossing an ethical line."

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