SAN ANTONIO, Texas - Scientists for the first time have directly confirmed that fat deposits in the arteries of teen-age boys can turn into heart-attack-causing lesions by the time they reach their early 30s.

In a report presented here Monday at the American Heart Association science writers forum, researchers also reported evidence of a genetic predisposition in some people that may account for why some fat deposits become lesions and some do not. The preliminary findings come from autopsies of 300 males 15 to 34 years of age.

If the results in the nationwide study hold up after all 1,800 planned autopsies are completed, physicians might be able to give children and teen-agers a simple blood test to evaluate their risk of heart disease. Confirmation of the findings would also effectively quash a longstanding debate over whether some children should be fed the same lower-fat diets recommended for adults.