Two years ago, Emily Rosa of Loveland, Colo., designed and carried out an experiment that challenges a leading treatment in alternative medicine. Her study, reported today in The Journal of the American Medical Association, has thrown the field into tumult.

Emily is 11 years old. She did the experiment for her fourth grade science fair.

The technique she challenges is therapeutic touch, in which healers manipulate what they call the ''human energy field'' by passing their hands over a patient's body without actually touching the patient. The method is practiced in healing centers and medical centers throughout the world, and is taught at prominent universities and schools of nursing.

Tens of thousands of people have been trained to treat patients through the use of therapeutic touch. Practitioners insist that the human energy field is real and that anyone can be trained to feel it.

But Emily asked a sort of ''emperor's new clothes'' type of question. Could therapeutic touch practitioners actually detect a human energy field? Her method was devilishly simple.