BOSTON (AP) - For the first time, scientists say they have used the ethically sensitive technology of therapeutic cloning to repair an inherited disease in a lab animal.

While still far from human use, experts say this demonstrates the potential power of the approach to correct many common illnesses that affect people.

Most of the steps in the work have already been accomplished individually in lab animals. Scientists have used so-called therapeutic cloning to make embryonic stem cells that can develop into many different kinds of tissue, such as muscle or nerves. But until now, they have not been put back into an animal to treat a disease.

The experiments involved repairing an immune system defect in mice. First, they made clones of the animals to harvest embryonic stem cells.

Next, they fixed the genetic defect in these stem cells. Finally they put the repaired stem cells into the adult animals, where they partially overturned the immune defect.

"This really is a tremendous confluence of very, very challenging technology, wrapping them all together into a model therapy," said researcher George Daley. "We are the first to do this all the way."

The experiments were conducted by Daley and Rudolf Jaenisch at the Whitehead Institute for Biomedical Research in Cambridge, Mass. Two reports on the work were to be posted online today by the journal, Cell.

"Putting it all together in sequence is dramatic," said Neil Theise, a stem cell biologist at New York University.

"The fact they are doing it in a model of a human disease is very canny, and certainly this will have a big impact on the public debate."

Therapeutic cloning starts with cells derived from test-tube embryos that are genetic twins of the recipient.

Many, including President Bush and some members of Congress, are opposed to cloning of all forms, including the therapeutic variety.

Some scientists, including Daley, have proposed calling the procedure "nuclear transplantation therapy" to avoid confusion with reproductive cloning, which is intended to produce a whole person.

The latest experiments were conducted on inbred mice that had severe immune deficiency because of a genetic defect that prevented them from manufacturing antibodies in response to infections.