BOB ABERNETHY: Sometime this month, scientists say they will announce that they have mapped almost all the human genome, the inherited instructions that tell our bodies what to do. The promise of the new knowledge is so vast, some researchers speak of a revolution in biomedicine, even disease-free long life. Meanwhile, scientists and ethicists worry about the moral questions the new technology could raise. In today's special report, we look at both the medical promise and the ethical issues of the human genome project.

It's been called the largest and most important project ever in basic scientific research, a 10-year-old international effort to find and map the body's three billion bits of inherited genetic instructions, the human genome.

The project has produced enormous hope for preventing and curing disease. Some say the human life span could be doubled. At the same time, there's intense moral concern about the possible effects. Who should get the new treatments, and could the whole human species be changed?

Perhaps no one is more optimistic about the promise of genetic medicine than Dr. Francis Collins, the head of the government-supported Human Genome Project at the National Institutes of Health.

Dr. FRANCIS COLLINS (NIH Human Genome Project): I think in another 20, 25 years, we should be able to prevent or cure most cases of cancer, of diabetes, of heart disease, of multiple sclerosis, of asthma.

ABERNETHY: But diseases are caused by the environment and our own behavior, as well as by heredity, so other observers are much more cautious.

Mr. DANIEL CALLAHAN (The Hastings Center): The claim has been made and repeated very often that this is going to provide the great key for understanding disease and, thus, they open the way to the cure of disease. So it's a very elaborate, bloated claim, even. I don't know that this will actually happen.

ABERNETHY: There is no argument about the magnitude of the knowledge already acquired. Inside nearly all the body's 100 trillion cells are long, twisted molecules of DNA called the human genome. The genome consists of different pairs of chemicals adding up to three billion bits of genetic information. What researchers have accomplished is to take apart the DNA and identify and put into sequence the segments of it that are called genes. Each cell contains all the tens of thousands of genes that give the directions for how the whole body develops and works. At the Whitehead Institute at MIT, director Eric Lander says this genome mapping is great, but just the beginning.

Mr. ERIC LANDER (Whitehead Institute for Genome Research): It's like having the parts list to a Boeing 747. You have the parts, but you don't know how to put them together to make an aircraft and you certainly don't know why from that an aircraft flies. The task of understanding the function of all of the genes in the body will probably occupy the next century.

ABERNETHY: But even now, even before scientists know exactly how each gene works, they know enough to say which defective genes invite what problems. For instance, in this gene sequence, one missing letter signals a genetic defect that could cause colon cancer.

Unidentified Man: This is the band of interest right there.

ABERNETHY: Specific genes have been associated with cancer, diabetes, heart disease, Parkinson's disease -- in all, nearly 4,000 diseases. And here the ethical issues begin. It's now possible to analyze the DNA from just one of your cells and create a genetic profile showing the diseases for which you might be at risk -- a kind of future diary. Many patients might want to know these risks if there were cures for the diseases, but what if there are not?

Mr. GEORGE ANNAS (Legal Ethicist, Boston University): Do you want to know that you're likely to get early Alzheimer's, for example, or colon cancer or whatever? Do you want to know that? I mean, I don't, for example.

Mr. RONALD COLE-PORTER (Pittsburgh Theological Seminary): If we know what the genes tell us about our future, will we be the same people? Will we be spontaneous and will we be free?

ABERNETHY: But assume you do have a genetic profile. Who should see it?

Your employer? Your insurance company, the government, a reporter?

Mr. LANDER: We desperately need legislation to protect genetic privacy. There is no legislation on the books that would protect anyone from invasions of their genetic privacy.

Dr. COLLINS: This is a matter of some urgency. People who are in a position of finding out that they're at risk for some illness, whether it's breast cancer or heart disease, are afraid to get that information, even though it might be useful to them, because of fears that they'll lose their health insurance or their job.

ABERNETHY: After genetic profiling, the next job is to discover how each gene functions or misfunctions and create treatments to prevent genetic-related disease. After that, many scientists predict cures for existing gene-related illness. The billions of dollars to be made from genetic medicine have brought private companies rushing into the field to do their own gene mapping and apply for patents on both their findings and the government's, which are available to everyone free on the Internet every day. Critics say no one should own life processes. Investors say patents give them protection that's necessary to pay for developing expensive new cures. Whoever develops the treatments, the possibility of wiping out scores of fatal diseases has raised the question: How long should we live? If preventing and curing genetic diseases could double our life span, would we really want to be 150? What might a centenarian say?

Mr. CALLAHAN: "I don't want to be 150. That was a big mistake. I should never have taken that drug. I'm 125 and I've had it. Enough's enough." Well, what are you going to do? Suicide, kill them off. You'd have a lot of you would have some real problems there.

ABERNETHY: Another issue: many scientists think it may become possible not only to prevent and cure disease but to enhance our children genetically, creating smarter or taller designer babies.