All too often, talk about altering genes raises science fiction images of giant ants, Andromeda strains and Frankenstein's monster. Such images have lingered.

Then, when scientists raised real concerns in the mid-1970s about possible risks of moving genes between species, Congress and the public became so concerned that some gene experiments were temporarily banned.

Now, there are worries that the same fears will arise with the advent of human gene therapy.

"There is plain irrational fear. I call it genophobia. Genoneurosis. Gene psychosis," said Arthur L. Caplan, head of the Center for Biomedical Ethics at the University of Minnesota. "You say 'gene' and people kind of lose their ethical bearings. They immediately assume that the clone of Adolph Hitler is coming over the hill."

So when scientists started talking seriously about altering genes in people to treat disease, even the research community got a little nervous. As a result, the federal government created a special review system to examine plans to plant genes in people. The review was more extensive than any ever conducted for a medical experiment, including trials as dramatic as putting an artificial heart in Barney Clark and others.

But genes have always been different, and there are many reasons for the fear, Caplan said.

"People just don't understand genetics very well," he said. "Anything they don't understand, they fear." Then there is the real history of eugenics, where the Nazis tried to improve the race by encouraging people with certain genetic traits to multiply and destroying others. And some people -- such as the Green Party in West Germany -- believe it just is not right to fool around with Mother Nature.

Leroy Walters, head of bioethics at the Kennedy School of Ethics at Georgetown University, is less certain that the public is afraid of genetics and points to a 1987 Lou Harris poll.

This poll of 1,273 people conducted for the congressional Office of Technology Assessment indicated that 83 percent of American adults favored using gene treatments to "cure a usually fatal genetic disease."

What's more, the poll found that 84 percent favored gene treatments that would "stop children from inheriting a usually fatal disease" -- essentially genetic alteration of their parent's sperm and egg, so-called germ-line therapy.

Support for the technology dropped only by half when the poll asked if techniques called genetic enhancement should be used to improve a child's intelligence (44 percent in favor) or physical characteristics (42 percent in favor).

"I think that when specific applications of genetic intervention are mentioned, like curing a usually fatal genetic disease, the public affirms those goals and is willing to use gene therapy," Walters said.

Even so, some researchers still worry.

"I think there is still a strong undercurrent of concern about mucking about with people's genes," said Paul Berg of Stanford University, winner of a Nobel prize in genetics and a central figure in the early debates about the hazards of genetic engineering. "I don't think it is very vocal, but I don't think it would take a lot to bring it to the fore."

W. French Anderson of the National Heart, Lung and Blood Institute believes that public acceptance of gene therapy is tied to what happens to the first patients. "The public's concerns will depend on whether we get a patient cured before we have a problem."

Critics such as Jeremy Rifkin, president of the Foundation for Economic Trends, have accepted the current gene treatments that only repair cells in a single individual but still object to germ-line therapy, the genetic manipulations that forever alter future generations.

"There are people who worry about the slippery slope," Caplan said -- the idea that once gene therapy starts, scientists will be engineering future generations. But "to block germ-line therapy down the road makes no sense when it might get rid of inherited diseases," he said.

Caplan, Walters and others agree, however, that the debate becomes far more complicated when discussing the possiblity of using gene enhancement to make a child taller or smarter. Most oppose that.

Scientists do not now have the techniques to either alter the germ line or enhance a child. These battles will be fought sometime in the future.