The scandal over delays in medical care for US veterans has put the spotlight on a sprawling bureaucracy struggling to cope with an influx of patients with new ailments after a decade of war.

The Veteran Affairs Department (VA) was already under scrutiny over its slow-moving health service, but allegations that a Phoenix hospital maintained a secret waiting list and that up to 40 veterans may have died as a result have sparked a furious reaction.

The disturbing claims have placed President Barack Obama on the defensive, but he has cited the strain of the wars in Iraq and Afghanistan as an aggravating factor.

"We all know that it often takes too long for veterans to get the care that they need. That's not a new development," Obama told a news conference Wednesday.

"It's been a problem for decades. And it's been compounded by more than a decade of war."

Out of 22 million veterans in the country, including those who served in World War II, nine million are enrolled in the VA's vast health care system.

The number of veterans receiving benefits and services has steadily grown in recent years and is expected to swell further as the United States pulls out of Afghanistan and older troops retire.

By 2015, the VA will be treating 6.7 million patients, an increase of nearly one million patients -- or 17 percent -- since 2009, according to the embattled VA secretary, Eric Shinseki.

- Gauntlet of red tape -

Apart from hundreds of thousands of troops who served in Iraq and Afghanistan, the VA must provide care for veterans from Vietnam who now have ailments related to old age.

The recognition of more than a dozen illnesses caused by the use of Agent Orange in Vietnam and a growing number of female veterans has further strained the VA's system, according to officials and experts.

The cost of the medical care and benefits for veterans is rising dramatically, with the VA funding represents a quarter of the Pentagon's budget, amounting to about $159 billion.

A third of the VA's budget is devoted to health services, while the remainder goes to pensions for disabled veterans, assistance to homeless vets, education and other benefits.

But veterans often find that gaining access to medical care requires running a gauntlet of red tape and bureaucratic hassles, with incessant delays.

The agency has a backlog of more than 300,000 disability claims, with patients reportedly facing waits of more than four months. The backlog peaked at close to 600,000 cases in 2012, and officials say the trend is moving in the right direction.

"My attitude is for folks who have been fighting on the battlefield, they should not have to fight a bureaucracy at home to get the care that they earned," said Obama.

His comment echoed almost word for word remarks made by his predecessors, Jimmy Carter and Ronald Reagan, in decades past -- a reminder that delays have been a persistent failing at the VA.

America's wars after 9/11 have generated a range of ailments and injuries, including traumatic brain injury and post-traumatic stress, that require medical specialists.

"Current veterans list a lot more conditions on their claims than in previous wars," said Veterans of Foreign Wars spokesman Joe Davis.

The number of veterans seeking treatment for post-traumatic stress and other mental health problems has increased markedly, from 927,000 in 2006 to more than 1.3 million in 2013.

The VA initially failed to grasp the scale of the casualties from the conflicts in Iraq and Afghanistan, and at one point only counted those directly wounded by enemy fire without taking into account those injured in training or near an explosion.

That oversight was compounded by a lack of coordination between the Pentagon and the VA, as the two departments often failed to share medical records of soldiers leaving the military.

And the VA only recently converted to a digital record keeping system, after losing time with inefficient paper files for years.

But even the agency's toughest critics acknowledge that the quality of the health care is not at issue.

Despite its flaws and shortcomings, the VA "provides world class health care once you get in the door," Davis said.