With troops returning home from Iraq and Afghanistan, the cost of medical care for veterans is expected to skyrocket in coming years. A study released Wednesday suggests that a huge chunk of those costs could be devoted to treating the invisible wounds of war.

The study focuses largely on the costs of caring for veterans from previous conflicts — mostly the Vietnam War and the Persian Gulf War — and it examines data from only one year, 2007. But what it found was telling: the Department of Veterans Affairs spent nearly three times as much on services for vets with mental illness or substance abuse than on those without such conditions.

Vets with mental health issues accounted for about one in seven using the VA’s health services but nearly one-third of the system’s costs.

Those findings, the study’s authors say, have important policy implications.

“The size of the veteran population with mental and substance use disorders is likely to continue to increase, as military operations in Iraq and Afghanistan decrease in size and service members leave the armed forces,” concludes the new study, conducted by RAND Corp. and the Altarum Institute. “Given the clinical complexity and health care costs associated with these disorders, identifying ways to increase efficiency while improving quality is critical.”

The number of veterans seeking mental health services has increased sharply. Last year, more than 1.2 million veterans were treated by the VA for mental health problems. In fiscal year 2004, the figure was roughly 654,000. The largest increase has been among veterans diagnosed with PTSD.

In the new study, more than half of the costs attributable to vets with diagnoses of depression, post-traumatic stress disorder and other conditions were not directly related to their mental health treatment. The veterans suffered from, say, hypertension or diabetes. But experts say the explanations for that can be complicated. In some cases, treatment for mental health conditions can contribute to physical problems; in others, physical health problems are later found to have underlying mental health explanations.

“This is a large and complex group of patients,” said Katherine E. Watkins, one of the researchers behind the study.

The VA is seeking to expand and improve its delivery of mental health services. The new study gives the department relatively high marks, saying that, even if there’s substantial room for improvement, the VA has performed well, providing a quality of care that is similar to or better than the care given to privately insured patients or those enrolled in Medicare or Medicaid.

The new assessment is far rosier than the one the VA recently got from its own workers on the department’s ability to handle the growing load. More than 70 percent of social workers, nurses and doctors working for the VA said in a recent survey that they lacked the staff and space to meet the needs of veterans seeking mental health care.

More than 37 percent said they couldn’t schedule an appointment in their clinics for a new patient within the 14-day standard mandated by the department.

The findings of the new study were published online Wednesday by the journal Health Affairs.