A private company striving to map the human genetic code reported today that it has completed a major step in the project - sequencing the genome.

Celera Genomics of suburban Rockville, Md., said it has finished the sequencing phase of one person_s genetic code and will now begin to assemble the genetic fragments into their proper order. The human genome is a biological map laying out the exact sequence of the estimated 3.5 billion pairs of chemicals that make up the DNA in each human cell. Those chemicals are arranged in specific ways to create the estimated 80,000 to 100,000 human genes, which in turn carry the instructions for all the body_s processes. Understanding the massive series of genes that provide the code for life has been a major project for both private and public organizations for several years, because it could serve as the foundation for developing new medical cures and preventions. Celera is a private company that is competing with government researchers to decode the human genome. But to do so, it uses portions of the genome already sequenced by the nonprofit Human Genome Project, which posts on the Internet each bit of DNA it completes decoding. The Human Genome Project has posted 2.3 billion subunits of DNA that it has decoded on the Internet for use by any scientist. In contrast to how Celera sequences DNA, the Human Genome Project fits the genetic puzzle pieces together as they are discovered, accumulating larger - and what it calls more accurate - pieces. The Human Genome Project also expects to complete a ``working draft'' of the genome later this year, and to publish a full genetic map on the Internet by 2003.