Walter McKenzie's assignment toward the end of the Cold War was to mop up after mishaps at a nuclear weapons factory. With a crew of other laborers from rural Georgia, he swabbed away leaks and spills inside the secret buildings, until one day his body became so contaminated with radiation that alarms at the factory went off as he passed.

"They couldn't scrub the radiation off my skin -- even after four showers," McKenzie, 52, recalled of his most terrifying day at the Savannah River nuclear weapons plant near Aiken, S.C. "They took my clothes, my watch and even my ring, and sent me home in rubber slippers and a jumpsuit."

Later, when doctors discovered the first of 19 malignant tumors on his bladder, McKenzie followed the same torturous path as thousands of nuclear weapons workers with cancer: He filed a claim for federal compensation. It was denied.

Unable to access secret government files, or even some of his own personnel records, McKenzie could not sufficiently prove that he was exposed to something that may have made him sick. Nor can most of the 104,000 other workers, retirees and family members who have sought help from a federal program intended to atone for decades of hazardous working conditions at scores of nuclear weapons facilities around the country.

Since its inception in 2000, the compensation program has cut more than 20,000 checks and given long-delayed recognition to workers whose illnesses were hidden costs of the Cold War's military buildup.

Yet, of the 72,000 cases processed, more than 60 percent have been denied. Thousands of other applicants have been waiting for years for an answer. Overall, only 21 percent of applicants have received checks. Even as the nation continues to close and dismantle many nuclear weapons sites, a growing number of those who helped build the bombs are turning to lawyers and legislators to argue they are being treated unfairly.

Many complain that the compensation process is slow, frustrating, even insulting. "You get exposed to something that's so bad you have to leave your clothes behind," McKenzie said, "then they try to tell you it's not their fault that you got sick."

Some evidence suggests the government has tried to limit payouts for budget reasons. Internal memos obtained by congressional investigators show the Bush administration chafing over the program's rising costs and fighting to block measures that would increase workers' chances of compensation.

But Labor Department officials who oversee the program say it has been successful, pointing to the large sums distributed: about $2.6 billion in payments in five years, far more than some early estimates. Missing or unreliable records and the murkiness of cancer science, the officials say, make it difficult to satisfy all the claimants.

"In a compensation program, you get benefits out to people who are eligible and you inevitably have to deal with the fact that some people are not eligible," said Shelby Hallmark, director of Labor's Office of Workers' Compensation Programs. "As for the assumption that the program is somehow trying to block people from getting compensation, nothing could be further from the truth."

David Michaels, a former Energy Department official who helped launch the program in the late 1990s, said it is designed to "bend over backward" to award compensation to deserving workers. "Most of the people who should be compensated are being compensated," said Michaels, now associate chairman of George Washington University's department of environmental and occupational health.

Still, Labor's management of the program has drawn bipartisan, and often fierce, criticism from members of Congress.