“We are not interested in quality of life,” Dr. Powell said in an interview. “We are just interested in whether you are able to survive this particular crisis.”

Anyway, she said, age has not been “a particularly sensitive discriminator for survival” in H5N1 flu. Many of its victims have been young.

Though allocating scarce resources is a perennial topic among ethicists and health officials, the authors say their guidelines are the first of their kind in the nation and could be a template for rationing in other catastrophes.

“This kind of thinking, as scary or even horrifying as it may seem, is absolutely critical and is much better done now than on the fly in the middle of a pandemic,” said Dr. Art Kellerman of Emory University, an expert on emergency medicine.

Dr. Kellerman, who was not connected to the study, said that a crisis like a flu pandemic was a matter of when, not if, and that he was “frustrated with people who want to pretend that it won’t be an issue or simply pass the buck to the emergency care physician.”

The guidelines confront that issue explicitly, recommending the appointment of “triage officers” to make ventilator decisions based on information about the number of incoming patients and their conditions, but who will not be involved in caring for them. If doctors and nurses caring for the sick must also make these triage decisions, the report says, the resulting stress can be “corrosive.”

Under the guidelines, “the person who is providing your direct care is not going to be the person who decides whether you stay on the vent or go off,” Dr. Powell said. “You need to know they are advocating for you. They cannot be looking out the door at how many people are waiting for care.”