Six weeks after arriving in Vietnam in 1967, Bruce McNeill stepped on a booby trap. The ground beneath him erupted with shrapnel.

McNeill recuperated in a U.S. veterans hospital for the next year, undergoing surgery, rehabilitation and more surgery. He says he was lucky: He suffered nerve damage but did not lose any limbs.

But that struggle for life would resume more than 25 years later.

In 1993, he discovered that a long-simmering hepatitis C infection had destroyed his liver. Without a transplant, the doctors said, he had a 50-50 chance of surviving two more years. He was 47.

Increasing numbers of veterans are hearing such news. The deadly virus, which is carried in the blood and attacks the liver, sometimes takes decades to reveal itself. It has infected almost 2 percent of adult Americans. But among veterans, especially Vietnam-era veterans, the infection rate is many times higher.

Depending on the population studied, estimates suggest 10 percent to perhaps 20 percent of veterans--a majority of them Vietnam veterans--may be infected. And most of them probably aren't aware of it.

"There are people out there very sick, and they don't know that they're sick," said Terry Baker, a Vietnam Veterans of America service officer who learned of his own hepatitis C infection in 1998.

The people most at risk for hepatitis C are those who have been exposed to another person's blood through transfusions, sharing needles and other risks.

America's wounded in Vietnam received 365,000 blood transfusions just from 1967 through 1969. The Vietnam War occurred before doctors realized how dangerous contact with another person's blood could be. No one had heard of hepatitis C, which didn't even get a name until 1989.

"In combat, there's no sanitary conditions," Baker said. "Everybody's either cut or bleeding somehow."

And there are other circumstances that left veterans disproportionately exposed to other people's blood, he said.

"Some of our lifestyles were a little off-base as well," Baker said. "There was drug abuse. There was promiscuity." Some studies suggest that a high number of sexual partners increases risk of infection.

He believes his own hepatitis C infection might have something to do with the anchor he had tattooed on his hand when he served aboard a destroyer during the Vietnam War.

Vietnam veterans are also particularly affected by the disease because of their demographics, said Teresa Wright, chief of gastroenterology at the San Francisco VA Medical Center. People in their forties are among the most likely in the general population to be diagnosed with hepatitis C, she said, because that group has been most exposed to risk factors. The hepatitis C problem among Vietnam veterans "is probably a reflection of the age group where hepatitis C is most common."

But many veterans are facing a struggle not only against the virus, but against the system. To be fully covered by Department of Veterans Affairs health care, a veteran has to show that an illness or injury can be traced to time in the service.

"How are these guys going to document they got hepatitis 30 years after the fact?" asked Tim Kirwan, a counselor with the Texas Veterans Commission office in Dallas.

Although many veterans say they have difficulty getting approval, about 50 to 60 percent of hepatitis C-related claims to the VA are granted, said department spokeswoman Laurie Tranter. And the agency is working to better define its policy on hepatitis C, she said.

Whatever the final policy, treating the problem will be expensive. Among those with hepatitis C, up to 85 percent will go on to develop a lifelong infection, and one in four of those will end up with cirrhosis and liver failure. The only treatment for that is a liver transplant.

About 2.5 million Vietnam-era veterans are living in the United States.

Veterans trying to link their infection to their military service face an almost impossible task, said Rep. Victor F. Snyder (D-Ark.). A Vietnam veteran and physician, Snyder has introduced legislation that would grant the presumption that hepatitis C infection is related to any veteran's service, provided the veteran meets certain general criteria.

"For every veteran who has hepatitis C, there is a point in time at which they acquired it," Snyder said. "It's not one of these things like a chronic back ailment.

"How do you prove when that time was?" he continued. "You're trying to prove it at a time in history when we could not test for the disease and didn't even have a name on it."

A similar bill has been sponsored in the Senate by Sen. Olympia J. Snowe (R-Maine).

Snyder acknowledges that many veterans had multiple risk factors, including intravenous drug abuse. "I've just concluded that the presumption ought to be with the veteran," he said.

McNeill, who lives in Mesquite, Tex., has no idea how he was infected. He had so many surgeries to repair the damage to his legs and right arm, he lost count. He returned from the war steeped in a volatile mixture of emotions: embarrassment for being wounded so early, guilt for having survived, a feeling of invincibility from living through a blast that should have killed him. He started using drugs.

"I could say I got hepatitis C from Vietnam, but I couldn't prove it," he said. In the end, he didn't have to. He received a liver transplant in 1994, covered by the military insurance that he receives for being more than 80 percent disabled from the war.

Other veterans have to appeal to the VA. Michael Newman, of Dallas, was at first denied his claim for coverage of his hepatitis C infection. Newman, who served in the Navy in the mid-1970s, also doesn't know how he was infected. He said the only exposure to needles and blood he can recall is the battery of injections and vaccinations he received while in the service.

Then last year, while leafing through a box of papers, Newman came across a letter from the Navy Regional Medical Center in San Diego, dated Dec. 18, 1973. The letter informed him that, after donating a unit of blood, he had tested positive for "hepatitis associated antibody."

"I cried," Newman said of his reaction upon seeing the letter. It was the proof he needed to receive coverage from the VA.

Baker, of Delaware, said veterans need to understand their risks of hepatitis, and he's founded an organization to raise their awareness of the infection.

A recent survey from his group, Veterans Aimed Toward Awareness, found that among 500 veterans surveyed, only about 40 percent had been tested for the virus. Most of the men surveyed were between the ages of 40 and 60. More than half were unfamiliar with the disease.

"It's smoldering out there," Snyder said. "It's going to cause more and more problems for people."