If ACTN3 suggests a child may be a great athlete, he said, parents should take a step back and nurture that potential Olympian or N.F.L. star with careful nutrition, coaching and planning. He also said they should hold off on placing a child in a competitive environment until about the age of 8 to avoid burnout.

“Based on the test of a 5-year-old or a newborn, you are not going to see if you have the next Michael Johnson; that’s just not going to happen,” Mr. Reilly said. “But if you wait until high school or college to find out if you have a good athlete on your hands, by then it will be too late. We need to identify these kids from 1 and up, so we can give the parents some guidelines on where to go from there.”

Boyd Epley, a former strength and conditioning coach at the University of Nebraska, said the next step would be a physical test he devised. Atlas plans to direct children to Epic Athletic Performance, a talent identification company that uses Mr. Epley’s index. He founded the company; Mr. Reilly is its president.

China and Russia, Mr. Epley said, identify talent in the very young and whittle the pool of athletes until only the best remain for the national teams.

“This is how we could stay competitive with the rest of the world,” Mr. Epley said of genetic and physical testing. “It could, at the very least, provide you with realistic goals for you and your children.”

The ACTN3 test has been available through the Australian company Genetic Technologies since 2004. The company has marketed the test in Australia, Europe and Japan, but is now entering the United States through Atlas. The testing kit was scheduled to be available starting Monday through the Web site atlasgene.com.

The analysis takes two to three weeks, and the results arrive in the form of a certificate announcing Your Genetic Advantage, whether it is in sprint, power and strength sports; endurance sports; or activity sports (for those with one copy of each variant, and perhaps a combination of strengths). A packet of educational information suggests sports that are most appropriate and what paths to follow so the child reaches his or her potential.