American and French scientists, in separate research projects, have uncovered genetic blueprints for the virus that causes AIDS, a major finding that is expected to assist basic studies of the deadly disease as well as aid efforts to detect, prevent and treat it.

The findings of a collaborative project initiated by the National Cancer Institute (NCI) with Harvard Medical School and two commercial laboratories will appear in the Jan. 24 issue of the British journal Nature, detailing the entire genetic structure of two samples of the AIDS -- acquired immune deficiency syndrome -- virus.

"This is a significant step forward in understanding how the virus works," Dr. Robert Gallo, head of the NCI laboratory here that discovered the AIDS virus last spring, said in an interview yesterday.

"Now we see the face of the enemy. We have the complete blueprint for the modus operandi of the virus," said Dr. William Haseltine of Harvard's Dana Farber Cancer Institute.

The researchers said that having the blueprint of various forms of the AIDS virus could have immediate applications in designing better, more accurate tests to detect infection. With genetic engineering techniques, it also will be possible now to isolate key fragments and mass-produce them in a way that "cuts the costs and the risks" of working with the hazardous AIDS virus itself, said NCI's Dr. Flossie Wong-Staal.

This would improve upon an initial antibody blood test to detect signs of past infection, a test that is expected to be approved within weeks.

The new research also gives more specific information for ultimately designing drugs to inhibit growth of the AIDS virus and possibly a vaccine to prevent the disease. Haseltine cautioned, however, "It is like having a model of a car without knowing exactly how it moves . . . . We can't say how fast this information will find its way into use."

He said that the genetic makeup of the AIDS virus was discovered "in record time" because of an unusual collaboration among scientists from two NCI laboratories, Harvard, E.I. du Pont de Nemours & Co. in Wilmington and Centocor Inc. in Philadelphia.

There was a race -- what one participant called a "dead heat" -- with other laboratories that are expected to publish similar discoveries soon. A group from the Pasteur Institute in Paris, which discovered an AIDS virus considered to be the same as the Gallo virus, will report its own study of the genetic sequence of their AIDS virus in the American journal Cell. It will be in the January issue, to be published next week, a journal spokesman said yesterday.

In addition, sources said that in coming weeks, groups from the California genetic engineering companies Chiron Corp. and Genentech Inc. also will publish their own genetic sequences for variants of the AIDS virus.

The multiple discoveries and other work will help scientists understand how much variability there is in the AIDS virus, a factor crucial to whether a vaccine will be possible.

The NCI project found that two isolates of the virus were each composed of four or five genes made up of more than 9,000 "base pairs," or building blocks, with only 1 percent variation in the arrangement. They expect more variation in other strains of the AIDS "retrovirus," which is made up of ribonucleic acid (RNA), not the more common deoxyribonucleic acid (DNA).

The NCI and Harvard researchers said that their initial discovery of the genetic structure of the AIDS virus, known as HTLV-III for Human T-Cell Leukemia Virus III, produced several surprises that provide intriguing leads for understanding how this virus dismantles the body's immune system by killing certain white blood cells. They found key differences between the genetic makeup of the AIDS virus and related HTLV viruses that instead cause the white cells to multiply, leading to cancer.

In the United States, 7,788 cases of AIDS had been reported as of Jan. 7, of which 3,687 were fatal.