WASHINGTON (AP) — Famous people don't often get involved with Medicare payment policy, but a Boston Marathon bombing survivor and a former U.S. senator who lost a leg in wartime service have joined an industry campaign to block new requirements for artificial legs and feet.

Medicare's mounting cost for those items in the last 10 years — even as the number of amputees was declining — has prompted scrutiny from government investigators.

Now, Medicare's billing contractors are proposing closer medical supervision of the independent technicians who sell and fit artificial limbs, as well as tighter rules for beneficiaries to qualify for high-tech devices that can cost as much as a car. The proposal is technical, but the industry says it will translate to diminished quality of life for beneficiaries at risk of being denied the latest technological advances.

With sign-waving amputees protesting at the Health and Human Services headquarters in Washington on Wednesday, the Obama administration was saying little. A Medicare spokesman refused to answer questions about the proposed changes, issuing a statement that the agency "believes that Medicare beneficiaries will continue to have access to lower-limb prosthetics that are appropriate" and the payment overhaul "is not meant to restrict any medically necessary prosthesis."

Officials made similar assurances in a meeting with representatives of the protesters.

Taking part in the demonstration was Boston Marathon bombing survivor Adrianne Haslet-Davis. Although far too young for Medicare, the ballroom dancer and motivational speaker said it's a cause "close to my heart."

"I'm here because America rallied around Boston, and I'm rallying around America," said Haslet-Davis, who lost her left leg below the knee.

Weighing in via a letter to HHS leadership was former Sen. Bob Kerrey. The Nebraska Democrat was awarded the Medal of Honor for combat in Vietnam, on a mission in which he continued directing his Navy SEAL unit after he was gravely wounded. He lost his right leg below the knee.

"They are attacking a problem that is nonexistent," Kerrey said in a telephone interview. "If you have a problem provider, shut him down; kick him out of the program. Why make it difficult for everybody else?"

The campaign is being led by the American Orthotic & Prosthetic Association, a trade group, alongside a broader amputee coalition that includes patients. Haslet-Davis and Kerrey said they are not being paid for their advocacy.

The industry group has several specific objections that involve emotionally charged issues and hinge on concerns about how the technical language of the proposal would be applied in real life. For example:

—An amputee who uses a cane, crutch or walker for limited purposes, such as getting out of bed at night to use the bathroom, will be limited to older-model artificial legs that are less functional. That particular example appears nowhere in the proposed policy, but AOPA Executive Director Tom Fise said he could see a scenario in which a Medicare billing reviewer would deny payment for an advanced prosthesis if the program had previously paid for a cane or walker for the same patient.

—A requirement that artificial legs and feet provide "the appearance of a natural gait" is being questioned as vague, unscientific and potentially restrictive. "There is no normal gait," said Dr. David Armstrong, a professor of surgery at the University of Arizona and diabetes expert. "That's just like saying there is a normal eye color." Armstrong serves as an unpaid medical adviser to the amputee coalition.

Bill Crowell, a Medicare beneficiary who lost both legs below the knee because of diabetes complications, said he's concerned about preserving access to the latest technology. He traveled to the protest rally from Richmond, Virginia, about 110 miles away.

"I don't think any citizen likes the idea of the government limiting their quality of life and what can and can't get covered by Medicare," Crowell said.

Although artificial legs and feet are a small part of Medicare's $600-billion-a-year expenditures, a 2011 inspector general's report found that Medicare spending for lower limb prostheses increased by 27 percent from 2005 to 2009, even as the number of beneficiaries getting them decreased by about 2,000 people. During those years, spending went up from $517 million to $655 million, even as improved diabetes care had reduced the number of amputations.

The report documented billing irregularities and led to questions about whether elderly patients whose physical activity is limited were being fitted with costly high-tech devices intended for younger active people. The wars in Iraq and Afghanistan have spurred a revolution in the design of artificial limbs.

Fise, the trade group executive, says that the industry has already addressed the concerns identified by the inspector general, and Medicare spending on artificial limbs has gone down since the report.

A public comment period on the proposed policy changes closes Monday. It's unclear when they would take effect.