The U.S. Patent and Trademark Office has turned down a scientist's controversial request for a patent on creatures that would be part animal and part human--bizarre life forms that no one has made before, but that might prove useful in medical experiments.

But unlike most patent office rejectees, the scientist, Stuart Newman, is celebrating. The New York Medical College biology professor never intended to make the animal-human hybrids. He applied for the patent to gain the legal standing to challenge U.S. patent policy, which allows patents on living entities.

The patent office ruled in part that Newman's invention is too human to be patentable. By doing so, it opened the door to a series of legal challenges available to all patent applicants--a path that could lead to the Supreme Court.

Newman hopes his appeals will force a judicial and congressional reassessment of the nation's 19-year-old policy of granting patents on life forms. That policy, based on a single court decision, has provided the foundation for today's $13 billion biotechnology industry.

Some patent experts this week criticized Newman for "abusing" the federal patent review system to bypass the legal avenues by which patent law is normally made and changed. But even some critics confirmed that the strategy appeared to be working.

In particular, said John Barton, a patent specialist at the Stanford University School of Law, the ploy has forced the patent office to acknowledge the relatively thin legal ice upon which its policies on life patents rest. The ruling also reveals the agency's apparent uncertainty about just how human a creature must be before it is no longer patentable, Barton and others said.

The patent office has argued that to grant patents on people would violate the 13th Amendment to the Constitution, which abolished slavery. But neither the patent office nor Congress has ever defined "human."

That question is of more than philosophical import today. Already, several patents have been allowed on animals containing human genes or organs. And just this week, scientists in Massachusetts said they were creating live embryos by combining cow and human cells.

"When we applied for this patent a year and half ago, people reacted to it as if it was some kind of science fiction scenario," Newman said. "Developments in the past year have shown that similar things are already on the table and being considered seriously."

In its rejection letter, the patent office says Newman's invention "embraces" a human being, but it does not say why other creatures with human components do not "embrace" a human being, said Washington patent attorney Patrick Coyne, who filed Newman's application.

"This puts a big question mark on all commercial interests involving human embryos and embryonic . . . cells," said biotechnology activist Jeremy Rifkin, a co-applicant on Newman's claim, who has rallied religious leaders against patents on life forms.

The agency concedes in its letter that in the Supreme Court's single foray into the topic--a 5 to 4 decision in 1980 allowing a patent on a microbe--the justices did not include humans on their list of nonpatentable life forms. But Stephen Kunin, the patent office's deputy assistant commissioner for patent policy, said the agency "believes" that Congress did not intend to allow patents on humans or on creatures that are essentially human when it passed the National Patent Act in 1956. The agency, however, offers no basis for that belief, Coyne said.

Biotechnology executives have said that without access to patents on gene-altered animals and other living entities, they would not make the investments needed to develop new drugs and other products. Yesterday, some criticized Newman's legal attack.

"The net outcome of this attempt may hurt valuable medical research and ultimately deny therapies for patients who need them," said Carl Feldbaum, president of the Biotechnology Industry Organization.

Undaunted, Newman yesterday filed an appeal to the patent office.

"Private ownership of inventions is not the only way progress has been made in the history of science and the history of medicine," Newman said.