The number of older kidney donors has more than tripled, and discard rates are less than a third of that in the United States, said Dr. Ulrich Frei, a German nephrologist who has compared the two systems. Studies have found no significant difference in survival rates for older patients in Europe and the United States, he said.

Dr. Frei said he found the discard rate in the United States “quite disturbing.” The reliance on biopsy is misplaced, he said, and valuable hours are wasted in the sequential search for a taker for a lower-quality kidney. That they wind up discarded, he said, is “a self-fulfilling prophecy.”

On Friday, the kidney committee plans to circulate a new proposal that would leave most of the system in place. As with the prior plan, the top 20 percent of kidneys would be matched to the candidates expected to survive the longest, placing older patients at a disadvantage. But the remaining 80 percent would still be allocated primarily by time spent on the wait list.

“It’s a compromise,” Dr. Ratner said. “I think it’s going to make very little difference.”

Dr. John J. Friedewald, the committee’s chairman, said it was impossible to please everybody when allocating limited resources.

“We want to maintain equal access and do better with this pool of kidneys,” he said. “But by changing allocation slightly and getting 10,000 more life-years lived, what is that worth? Is it worth slightly decreased rates of access for certain groups of people? That’s what we go back and forth trying to decide.”

In August, as the committee finalized its recommendation, a group of researchers proposed yet another allocation algorithm in the American Journal of Transplantation. It would give individuals in different age bands an equal chance to get a transplant in a given year. But it would drive the best kidneys to the youngest recipients.

A lengthy public comment period will follow Friday’s release of the new proposal. The organ sharing network’s board is not expected to vote on a plan until at least June, and possibly much later.