Scientists used a manipulated cold virus to transfer a normal human gene directly into the cells of living animals, in what they believe could a step toward genetic treatment of respiratory diseases such as cystic fibrosis.

In a study published Friday, researchers at the National Institutes of Health said they used an inactivated virus of the common cold to carry the human gene into the lung cells of live rats and that the transferred gene then performed its normal function.Applied to humans, the technique eventually may be used to correct the genetic flaw that causes the lung problems in cystic fibrosis and in a form of inherited emphysema called alpha-1-antitrypsin deficiency, said Dr. Ronald Crystal, director of the pulmonary branch of the National Heart, Lung and Blood Institute.

"The two most common lethal hereditary diseases in the United States are alpha-1-antitrypsin deficiency and cystic fibrosis," said Crystal. "Both are lethal because of the respiratory manifestations."

If a way could be found to correct the flawed genes in the lung tissues of victims of these diseases, the fatal effects of the disorders could be prevented, he said.

But to do this, he said, a new gene transfer procedure was needed.

"The techniques used for gene transfer up to this point have been to take cells out of the body, modify the cells and then put them back," Crystal said in an interview. "For the lung we can't do this."