A government-funded study in which poor black and Hispanic boys were given a now-recalled diet drug to test for violent tendencies is being criticized as risky and racist. The federal government has launched an investigation.

Scientists at an institute affiliated with Columbia University were testing the brain chemistry of 34 boys using fenfluramine, which has since been taken off the market because of suspected links to heart-valve damage in adults. It is the "fen" in the diet drug combination fen-phen.Critics say the experiments, conducted in 1994 and 1995, offered no medical benefits and put the children at risk.

"These racist and morally offensive studies put minority children at risk of harm in order to prove they are generally predisposed to be violent in the future," said Vera Hassner Sharav, director of Citizens for Responsible Care in Psychiatry and Research.

The researchers defended their efforts as a legitimate attempt to understand the roots of violence.

The children were given a single fenfluramine pill and were kept in a hospital bed for at least five hours with a catheter in their arm while blood samples were taken. They were without food for at least 17 hours.

The boys all had older brothers who were juvenile delinquents, and the scientists wanted to know whether levels of serotonin in the brain could signal aggression. Fenfluramine induces the brain to release serotonin.

The boys' parents signed consent forms for the research at the New York State Psychiatric Institute.

Similar research, conducted by Queens College and Mount Sinai School of Medicine, is also under fire. That project used fenfluramine on 66 boys of various ethnicities who had been treated for attention-deficit disorder.

The institute, which reached no firm conclusions in a study published in September, issued a statement Thursday saying its research tried to identify factors that could trigger aggression "in a population at risk for the development of antisocial behavior."

Fenfluramine and a chemically similar diet drug, Redux, were pulled from the market because they were linked to potentially deadly heart valve damage. Earlier this month, however, a large study found no sign that brief use of Redux causes dangerous heart value problems.

Queens College, which is part of the City University of New York, said its study "posed no danger to children. . . . No child was harmed in any way."