The first task for Dr. Gale and the Soviet physicians was to determine, using the biological approach, how much radiation patients had received. Dr. Gale suggested to Dr. Baranov that patients whose dose of radiation was around 500 rads - the average dose that causes irreversible damage - should receive transplants (one rad is about 100 times that of a chest X-ray). On that first morning, one patient was clearly suitable for a transplant, and Dr. Gale helped perform it.

Those who had been exposed to so much radiation -as high as 1,200 to 1,500 rads - and the subsequent organ damage that a transplant would not help were given the best supportive care the doctors could offer: antibiotics, transfusions, pain killers. The doctors treating them and other patients wore no special protective clothing, only sterile gowns, hats, masks and cloth booties over their shoes. They did, however, check themselves with a Geiger counter every night before leaving the hospital. (Once, the shoes worn by a member of the transplant team were contaminated, but no one knew the source.) Dr. Gale realized immediately that Drs. Champlin, Terasaki and Reisner would be of great help. The Russians agreed. (They would be given visas upon their arrival in Moscow, which possibly made Dr. Reisner the first person traveling on an Israeli passport to arrive without a visa; the Soviet Union does not have diplomatic relations with Israel.) An office on the sixth floor of the hospital became the headquarters for the doctors, and a routine was quickly established. Early each morning, someone in the Occidental office at the World Trade Center in Moscow called Dr. Gale to read him the night's telexes concerning that day's arrivals of medical equipment and supplies (they came daily from all over Europe and the United States). Dr. Gale then informed Dr. Baranov and the physicians from the Ministry of Health. As incoming packages weighed anywhere from a few ounces to a ton, the people from the ministry needed to know ''whether to send a bike or a tank to the airport,'' Dr. Gale recalls. At about 9 A.M., Drs. Guskova, Baranov and Gale (as well as Drs. Champlin, Terasaki and Reisner after they arrived) met to discuss the patients. Around 11, the five hematologists doing the direct patient care came in individually with their charts to report the patients' status. By 1 P.M., their reports were finished. Then Dr. Gale and the others went to see the most critically ill. At 5 P.M., the physicians met again to go over the day's work, finishing at about 9 P.M.

During dinner, the foreign team continued to discuss the patients. Then Dr. Gale would spend several hours on the phone, making arrangements for supplies and equipment to be gathered and shipped. The laboratories of Drs. Terasaki and Reisner had to be set up and equipped and, in addition, Dr. Gale had a separate $800,000 shopping list. He called Dr. Hammer's assistant, Richard D. Jacobs, in Los Angeles, who, in turn, called pharmaceutical companies and medical equipment manufacturers. Their response was quick. For instance, Baxter Travenol, a Deerfield, Ill., company, tracked down three CS 3000 blood separators (each costing from $40,000 to $50,000) in Switzerland, France and Maryland, and arranged for their shipment (as well as the flights of two technicians from England and Belgium to operate them) to Moscow.

Dr. Gale generally got to sleep around 2 A.M., often to be awakened by an international operator putting through a call placed hours earlier. Most mornings he was up at 5 for more phone calls. Then he would go running, as he does no matter where he is, for about 45 minutes.

There were, at first, practical differences between the way the Americans and the Russians analyzed a patient's condition. Western physicians usually go over everything on a patient's chart. The Russians, Dr. Gale recalls, ''only focused on the important findings, but I needed everything. Otherwise, it was a seemingly random presentation of data, and that was a problem for me.'' Eventually he was able to make a chart of each patient's progress and to persuade the Russians to go through them one by one.

A week after his arrival in Moscow, the Soviet team informed Dr. Gale that there were an additional 16 in the same condition as the first 19. Also, about 260 less-severely affected accident victims were in Hospital No. 6. (Many radiation burns, says Dr. Gale, do not show for a week or two.) Yet even with a virtual doubling of the patient load, things moved quickly. At the end of a week, the doctors knew who else could receive transplants and had begun performing them, usually with Dr. Gale or Dr. Champlin working with a team of Soviet physicians and nurses. The international team did seven bone marrow and three fetal liver transplants. By May 15, all the transplants were completed and the first phase of work was over.

Before Dr. Gale left Moscow on May 16, the Ministry of Health asked that he hold a news conference, suggesting that he be the only participant and that there be only a written statement and written questions. Dr. Gale insisted that the press should be able to ask whatever they wanted. He felt a Soviet physician should be on the podium as well. He was, therefore, joined by Andre Vorobiev, the hematologist. Dr. Hammer, who had arrived on May 13 with a planeload of medical supplies and equipment, also joined him.