Get ready to add white-frocked scientists to the ranks of civil rights and anti-war activists who’ve marched on Washington.

Thousands of prominent cancer and other medical researchers will rally in the nation’s capital Monday to protest federal funding cuts that began several years ago and were accelerated by additional forced reductions taking effect under the congressionally mandated process of sequestration.

“It’s really come on top of a fairly extended period of flat funding, which has eroded the purchasing power of biomedical dollars,” said Roy A. Jensen, director of the University of Kansas Cancer Center, who will join the demonstration. “It’s almost like the final push over the edge. I know a lot of labs are having to lay people off and not pursuing promising scientific leads.”

Influential scientists say the United States has fallen to 10th place in medical research spending as a percentage of its total economy, at a time when China, Britain, Singapore, India and other countries are increasing their investments. They say the pace of breakthroughs in lifesaving treatment of cancer, HIV/AIDS and other major diseases will be slowed unless the decline is reversed.

“The cuts in federal funding as they’re being put into play are unraveling one of the greatest biomedical-research enterprises in the history of the world,” said Edward J. Benz Jr., head of the Dana-Farber Cancer Institute in Boston, which is affiliated with Harvard Medical School. “These kinds of draconian, across-the-board cuts are really cutting into the meat of what we do.”

The rally is being organized by the American Association for Cancer Research, which Monday morning will suspend its annual convention in Washington and ask 15,000 attendees to gather outside the Carnegie Library at Mount Vernon Square, about a dozen blocks from both the White House and the U.S. Capitol. Busloads of scientists from New York, Pennsylvania and other states are expected to join the demonstration.

Democratic Reps. Chris Van Hollen of Maryland and Rosa DeLauro of Connecticut are scheduled to address the rally, along with Francis Collins, director of the National Institutes of Health, and survivors of cancer, AIDS, diabetes, heart disease and other serious illnesses.

Annual federal funding of the National Institutes of Health, the Bethesda, Md.-based agency that finances most medical research in the country, has flat-lined at about $30 billion since 2010, which means that inflation-adjusted spending fell by 6.3 percent in that period. The forced cuts of 5.1 percent will trim an additional $1.5 billion this year, with effective funding down 11.4 percent.

The National Cancer Institute, the largest of NIH’s 27 centers, gets about $5.1 billion a year, or more than one-sixth the total NIH funding. It stands to lose $260 million this year because of the forced budget cuts, enough to finance the work of 575 scientists and lab technicians. Ninety percent of its budget is spent on research.

NIH research grants, which go to hundreds of universities, hospitals, pharmaceutical firms and other recipients across the country, range from $100,000 to $15 million, with the average grant at $450,000.

William Nelson, director of the Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins University in Baltimore, said he’ll join the protest march to help ensure the nation’s brightest young minds don’t abandon science for lack of support.

Nelson said many post-doctoral researchers and other young scientists are encountering greater difficulties obtaining grants than more seasoned peers because their track records are less extensive.

“If we lost a generation of the most talented thinkers, we are going to be paying the price for decades to come,” Nelson said. “It is very hard to get funds at the beginning of your career.”

Jon Retzlaff, policy chief with the American Association for Cancer Research, said he and others are holding the rally to demonstrate that medical research must remain a national priority.

“We’ve reached a crisis moment in supporting medical research,” Retzlaff said. “There’s never been a better time of pursuing scientific opportunity, but we are falling backward in our ability to really pursue it.”