Younger patients would be more likely than older ones to get the best kidneys under a proposal being considered by the nation’s organ transplant network.

The new policy would replace the present first-come-first-served system and is intended to provide better matches between the life expectancies of recipients and the functional life of donated kidneys.

“Right now, if you’re 77 years old and you’re offered an 18-year-old’s kidney, you get it,” said Dr. Richard N. Formica, a transplant surgeon at Yale University and a member of the panel that wrote the proposed policy. “The problem is that you’ll die with that kidney still functioning, while a 30-year-old could have gotten that kidney and lived with it to see his kids graduate from college.”

Under the proposal, patients and kidneys would each be graded, and the healthiest and youngest 20 percent of patients and kidneys would be segregated into a separate pool so that the best kidneys would be given to patients with the longest life expectancies. The remaining 80 percent of patients would be put into a pool from which the network that arranges for organ matches, called the United Network for Organ Sharing, would try to ensure that the age difference between kidney donors and recipients is no more than 15 years.