DALLAS (AP) _ Boys as young as 15 can begin to experience clogged arteries, according to a new study that says long-range prevention of heart disease must begin in adolescence.

Researchers led by Dr. Henry C. McGill Jr. of the Southwest Foundation for Biomedical Research in San Antonio pored over the autopsies of 760 young men and women who had died in accidents, homicides or suicides.

Arterial blockage was found in 2 percent of the 15- to 19-year-old boys who were studied, and in about 20 percent of the men ages 20 to 34. Even though a small number of the teen-agers had clogged arteries, researchers were surprised to see any at all.

McGill said the condition _ even in men as young as those studied _ would likely lead to a heart attack by the time they were in their 40s.

``They're not probably going to get a heart attack for another 10 or 15 years, but this would sure be a good time to start preventing it,'' said McGill, whose results appear in this week's edition of Circulation, a journal of the American Heart Association.

The data was collected over a seven-year period ending in 1994. Researchers analyzed blood cholesterol levels and measured plaques in one of the key blood vessels leading to the heart, the left coronary artery, where blockages are known to occur.

Several studies already have shown teens are not too young to suffer the physical effects of dangerously high cholesterol levels. High cholesterol often leads to plaques along the arterial walls, which then encourage blood clots that may lead to a heart attack or stroke.

Dr. Bruce Brundage, a cardiologist at St. Charles Medical Center in Bend, Ore., said the affected males probably suffered no ill effects from their slowly clogging arteries, especially because teen boys often feel like they're in top physical shape.

But Brundage, who was not involved in McGill's study, said the latest findings offered more evidence that the same risk factors for heart disease _ high cholesterol, high blood pressure, smoking _ known to put older people in jeopardy also affect the young.

``It's more confirmation the disease process starts earlier in life and it's progressive,'' he said.

In addition, McGill discovered a gender difference: none of the teen-age girls studied had blockages, and only 8 percent of the women from 20 to 34 had the severe arterial buildup found in the male group.

Brundage suggested that estrogen may protect some women from arterial clogging, but said further research is needed.