(AP) - Two research groups have identified the first gene known to suppress obesity and regulate the burning of calories - a find that could lead the way toward a drug that keeps people trim.

The gene, known as Mahogany or the MG gene, was discovered in mice. "Mahogany" refers to the animals' brown fur.

It is the sixth gene found to be implicated in obesity. But researchers said it is the first discovered to regulate metabolism and the expenditure of energy.

In one of two studies published in last Thursday's issue of the journal Nature, scientists at Millennium Pharmaceuticals in Cambridge, Mass., tested groups of mice with normal and mutated MG genes. They fed the mice diets with varying percentages of fat.

Mice with mutated MG genes did not gain weight regardless of whether they ate high-fat diets or low-fat ones. Mice with normal genes gained weight on high-fat diets.

Researchers said they were optimistic that the gene would play the same role in humans but cautioned that it has been demonstrated only in mice.And although the findings suggest it plays an important role in diet-related obesity, which afflicts most of the 54 percent overweight American adults, obesity is thought to more than a matter of genetics.

''Obesity is a complex problem for which diet, exercise and biology all are important,'' said Craig Warden, a geneticist at the University of California at Davis.

That's one reason why it could be several years before the researchers can transform their discovery into a fat-busting drug.