In a call with reporters Monday, Francis S. Collins, director of the National Institutes of Health, said the NIH was bracing for about $1.6 billion in cuts as a result of the sequester, affecting research into such diseases as cancer, influenza and Alzheimer's disease.

Hundreds of research grants would go unfunded, he said, and some 20,000 highly skilled workers would lose their jobs. He also expects to have to turn away patients from the NIH's clinical center, which allows people who have exhausted their treatment options to participate in clinical trials.

"I am a bit disheartened about this," Collins said. "It is a paradoxical thing that we are both at a time of remarkable and almost unprecedented scientific opportunity, and we‘re also at a time in the United States of unprecedented threat to the momentum of scientific progress."

The current budget for the NIH is $30.8 billion.

This post has been updated.