Washington ? The book of genetic instructions for the human body is complete to an accuracy of 99.99 percent, a scientific achievement once deemed impossible but now considered the foundation for a new era of medical advances, an international research team said Monday.

With the entire sequence in hand and available to scientists worldwide, experts predicted it would lead to new drugs, better forecasts of people’s health and new ways to treat or prevent many of the most devastating human illnesses.

A joint statement from the leaders of the six nations, including President Bush, said the genetic map “provides us with the fundamental platform for understanding ourselves from which revolutionary progress will be made in biomedical sciences and in the health and welfare of humankind.”

The group, along with a competing private effort, completed a rough draft of the genome in 2000, but that draft included thousands of gaps in the long sequence of DNA base pairs. Now all but 400 of those gaps have been closed.

“After three billion years of evolution … we have before us the instructions set that carries each of us from a one-celled egg through adulthood to the grave,” said Dr. Robert Waterston of the International Human Genome Sequencing Consortium. “It is written in an arcane language and encompasses a complexity that we are just beginning to understand.”

The genome is composed of about 3 billion pairs of DNA chemicals within 24 chromosomes. The genes that control the body’s development, growth, functions and aging are made of specific sequences of these chemical pairs. A small change in these sequences can be enough to cause disease.

By identifying the correct and healthy sequence of base pairs, researchers hope to be able to find the disease-causing genetic flaws that could yield to treatment.

Scientists are still uncertain how many genes there are in the genome, but most believe it is about 30,000. This number is expected to be refined with more research.

Announcement of the completed sequence comes just days before the 50th anniversary of the discovery of the double helix structure of DNA by James Watson, an American, and Francis Crick, a British biophysicist. They shared the Nobel Prize for the work.

Watson, who was the first director of the American sequencing effort, said at Monday’s news conference that his decision to devote 3 percent of the genome research effort to studying the ethical consequences of the gene sequencing may have been “the wisest decision that I made.”

He said there were concerns that if the research identified people with a genetic predisposition for disease it could lead to discrimination in employment and in other elements of life. Forty states have now passed laws forbidding genetic discrimination and federal laws have been proposed.

Dr. Francis Collins, head of the National Human Genome Research Institute, said the complete sequence of the genome is just the beginning of the genetic revolution. Researchers now will use the sequences to try to speed identification of genes that cause cancer, diabetes, heart disease and other disorders and then to develop drugs that either prevent or treat the disorders. Some disorders might be treated by manipulating or replacing flawed genes, he said.

It eventually may be possible to provide the unique genetic sequence for each patient and then to tailor therapy or prevention care for that specific person, the experts said. This could relieve some of the side effects caused by broad spectrum drugs.

The Department of Energy is now applying skills developed in the human project to study the fundamental life processes of bacteria and other microbes. This, in turn, could lead to microbial solutions for pollution control, removing carbon dioxide from the atmosphere and developing new energy sources, said Aristides Patrinos, head of the DOE program.