WASHINGTON — Increasing numbers of American troops have left the military with damaged bodies and minds, an ever-larger pool of disabled veterans that will cost the nation billions for decades to come — even as the total population of America’s vets shrinks.

Despite the decline in total vets — as soldiers from World War II and Korea die — the government expects to be spending $59 billion a year to compensate injured warriors in 25 years, up from today’s $29 billion, according to internal documents obtained by the Associated Press. And the Veterans Affairs Department concedes the bill could be much higher.

Why?

Worse wounds. More disabilities. More vets aware of the benefits and quicker to file for them.

Also, ironically, advanced medical care. Troops come home with devastating injuries that might well have killed them in earlier wars.

Time is also a factor when it comes to disability compensation costs. Payments tend to go up as veterans age, and an increasing number of soldiers from the Vietnam War will be getting bigger payments as they get older and are less able to work around their disabilities.

The number of disabled veterans has jumped by 25% since 2001 — to 2.9 million — and the cause really is no mystery.

“This is a cost of war,” a deputy director at the American Legion, Steve Smithson, said. “We’re still producing veterans. We’ve been in a war in Iraq for five years now, and the war on terror since 9/11.”

VA and Census Bureau figures show the previous six-year period, before hostilities in Afghanistan and Iraq, saw a more modest increase of 4% in the number of disabled vets. Veterans can make claims for disability benefits long after their military service has ended.

Today’s veterans — disabled or not — number nearly 24 million. That population is projected by the VA to fall under 15 million by 2033, mostly because of dying World War II and Korean War vets. But costs are expected to rise.

Inflation accounts for a big chunk of the increase. But even when the VA factors out inflation, the compensation for disabled veterans would still grow from $29 billion to $33 billion in today’s dollars — a more than 10% increase. And the department acknowledges the estimate could rise by 30%.

VA officials were not eager to talk about reasons for the increases. They declined several requests for interviews. In a written response to a handful of questions, the agency noted a few factors at play in the rising costs, such as the aging veterans population, an increase in the number of disabilities claimed, and the severity of injuries sustained.

Outside experts provided more insight.

The American Legion’s Mr. Smithson says the Iraq and Afghanistan wars are resulting in more severe injuries — amputations and traumatic burns — the kind of injuries that troops in Vietnam and earlier wars would not have survived.

Mr. Smithson says today’s veterans also are filing claims for more disabilities.

“People are more aware of the benefits they are able to file for (because of) better outreach,” Mr. Smithson said. “It’s not like the WWII generation and Korean War generation where they weren’t aware of what they could file for, and they were also reluctant to file if they didn’t think they needed it.”

Iraq veteran Christopher Bain filed for about 10 disabilities after his tour in 2004. Mr. Bain came under mortar fire outside Baghdad and was hit several times. He successfully fought doctors who wanted to amputate his left arm. But 10 operations later, he still needs help getting dressed each day. An electrical stimulator implanted in his upper buttocks helps dull the pain from his injuries.

“It’s hard, you go through certain periods of remorse,” said Mr. Bain. “I am never going to be the man I once was.”