The Japanese captors routinely marched human guinea pigs to the middle of a dusty field here 40 years ago, stripped them naked and blasted their buttocks with germ-laden shrapnel.

They hurled earthenware "bombs," containing millions of plague-carrying fleas, at others before cutting them up alive and without anesthetic to study the effects of disease on the vital organs.

Still other victims were injected with anthrax, cholera, smallpox and syphilis bacteria or subjected to marathon X-ray sessions that destroyed their livers to test the human body's capacity to absorb radiation.

Yet, according to Han Xiao, a local government official, and other accounts of the period, these grisly scenes only begin to convey the atrocities that grew out of experiments conducted on humans in World War II by the 731st Regiment, a clandestine germ warfare unit of the Japanese Imperial Army then headquartered here on the windswept prairies of Manchuria.

Han, who has spent the past 10 years trying to unravel the secrets of Japan's "Devil's Brigade," says the "cruelest thing the Japanese did" was to experimentally kill more than 3,000 Chinese, Korean and Soviet prisoners of war with biological and gas weapons at the Harbin germ factory.

But Han, whose investigation is part of a Chinese policy to document all past war crimes committed against China, adds that the gruesome devices developed here, and at other satellite units of the 731st throughout China, were then widely used by the Japanese against Chinese and Soviet troops and Chinese civilian targets during the fighting in Manchuria and Inner Mongolia.

Beyond that, Chinese and, more recently, some Japanese and American researchers have alleged that the macabre story of the Devil's Brigade leads to a tangled legacy of germ warfare involving the United States. It features a secret deal under which responsible Japanese officers were allegedly freed from war crimes prosecution by American military authorities after agreeing to hand over mountains of meticulous testing results.

In contrast to the Nazi death camps in Europe in World War II, Harbin's holocaust left no surviving victims to tell the tale. Han and his team of investigators have pieced together their picture of atrocities by methodically sifting through human bones and other debris left among the ruins of the 731st's camp. They have also interviewed many of the 500 villagers still alive who were forced to serve as laborers at the germ factory.

Masquerading as a water sanitation unit, the Devil's Brigade carried out its ghoulish work behind the high red brick walls of a 2 1/2-mile-square compound on the southeastern edge of Harbin. Today, the 731st's drab, squat administrative building houses Harbin's No. 25 Middle School, and the muddy schoolyard is dotted with swings, chinning bars and basketball hoops.

Strangely, there is no museum of the kind used to document wartime atrocities elsewhere in China. Weathered wooden tablets on the germ factory's bombed-out ruins state cryptically, in Chinese: "Evidence of crimes committed by the invading Japanese militarists."

Beginning in 1940, Han Xiao said, roughly 600 "logs," as the Japanese called their human guinea pigs because of their importance as basic building blocks for research, were brought here, usually at night. They were then marched through a long tunnel to jail cells at the rear of the compound, where they were fattened up on a special diet of meat and vegetables to ensure better testing results.

Under the direction of Lt. Gen. Shiro Ishii, an Army surgeon, the human laboratory animals were used with grotesque economy in search of preventive remedies for common battlefield diseases. Chiefly, though, Ishii and his fellow officers were looking for an array of cheap, effective weapons that they believed were essential for victory against the United States and its allies.

Among the more than 100 types of experiments conducted, the "logs" had their veins pumped full of horse blood in a primitive attempt to find a substitute for human blood. Others had their limbs frozen solid in subzero temperatures and then defrosted in vats of scalding water to look for clues for the treatment of frostbite, a method that frequently caused flesh to crumble off the bone. Reduced to physical wrecks after repeated experiments, survivors were often dissected alive, their vital organs thinly sliced and placed on glass slides for study under a microscope.

After leading haunted lives in Japan since the war, a handful of former members of the Devil's Brigade have stepped forward in recent years with accounts of the atrocities at Harbin. Few appear to have developed an immunity to the memories.

When the Soviet Army swept through Manchuria in August 1945, the actitivies of the 731st were brought to a dramatic finale, but the secrets of Harbin's human hell remained closely guarded. After Ishii had ordered his men to gas the remaining 150 "logs" and burn their corpses, the camp's laboratories and most of its buildings were destroyed with dynamite charges.

Apart from a handful of Japanese captured by the Russians and later sentenced to prison terms at war crimes trials in the Soviet Union, most of the 2,600 members of the 731st and their families escaped to Japan. In his final act of command, Ishii reportedly swore his men to secrecy and instructed them to "live in the shadows" for the good of Japan and their own welfare.

According to recent accounts by Japanese and American journalists, based on documents obtained from the Pentagon under the U.S. Freedom of Information Act, the U.S. military establishment struck a secret pact with the Devil's Brigade commander that granted Ishii and his subordinates immunity from prosecution by the Allies in the Tokyo war crimes trials.

In return, Ishii reportedly handed over 8,000 slides of tissue from human and animal dissections and other information, which the recent accounts suggest was stored at Fort Detrick in Frederick, Md.

According to the documents quoted, American military authorities regarded the information as "invaluable" and were eager to keep it from falling into the hands of the Soviet Union. Because of the moral and ethical constraints governing human experimentation in the United States, the documents are quoted as saying, the information could not have been otherwise obtained.

A Pentagon spokesman declined to comment, saying the Defense Department had "no historical documentation" on the subject.

Whether the United States did anything with the material it allegedly obtained from the Harbin experiments is a matter of controversy. An article in the U.S. publication Bulletin of the Atomic Scientists 18 months ago, which quoted U.S. military documents, said, "It is known that some of the biological weapons later developed by the United States were at least similar to ones that had been part of the Japanese project," including a method for infecting bird feathers with contagious diseases.

During the Korean War, China repeatedly charged that the United States was using germ warfare against it, a charge consistently denied by Washington and never substantiated. A Japanese researcher, Keiichi Tsuneishi, professor of the history of science at Nagasaki University, charges that there is strong "circumstantial evidence" to suggest that the U.S. military used the data obtained from Ishii to mount germ warfare experiments during the Korean War. But Tsuneishi acknowledges that there is no direct evidence of this.

In Harbin, Han Xiao said that the members of the Devil's Brigade, in their haste to flee from advancing Soviet troops, "released all their laboratory animals, among which there were many rats contaminated with plague." As a result, he explained, "they brought a big disaster to this area" when the disease swept through local villages in late 1945, killing more than 150 people.

According to Han, roughly 500 Americans were interned in Harbin during the war. Contrary to the speculation of some Japanese and American reports, however, Han asserted that none of the Americans were used as human guinea pigs by their Japanese captors. "The timing is all wrong," he said, because the human experimentation had largely stopped by the time the Americans, who were released before the end of the war, arrived here in early 1945.

Harbin's chamber of horrors was depicted in gruesome detail in "The Devil's Gluttony," by novelist Seiichi Morimura, Japan's best selling book last year. The book, and a sequel, have now sold more than 2.5 million copies--at a time when books, magazine articles and films giving relatively sympathetic treatment to the Japanese role in the war have gained increasing popularity in Japan.

According to Morimura, most members of the 731st took their vows of secrecy seriously. Caught in the crosscurrents of war and peace, many eked out livings in postwar Japan tortured by memories of atrocities. However, some of the regiment's top leaders, including Ishii, who died of cancer in October 1959, appear to have been less repentant, leading lives of relative prominence and wealth.

Shortly after they returned from Harbin, two of Ishii's key colleagues, who died recently, founded the Japan Blood Bank, the forerunner of the Green Cross Corp., a leader in Japan's sophisticated biotechnology industry. In April, company officials confirmed, Green Cross applied to the U.S. Food and Drug Administration for approval to manufacture and market its artificial blood in the United States.

"For people who don't know anything about war," one former Japanese medical officer who conducted poison gas experiments in Manchuria said, "it may be a shocking thing." But during World War II, "Gas was widely known among the Japanese as a potentially dangerous weapon and the study was one important element" in Japan's military defense.

Today, this man, who did not want to be identified, is a practicing physician and, for most of his career, taught at one of Japan's most prestigious medical colleges.

Prof. Tsuneishi, the author of a book on Japanese germ warfare, said that despite the equivalent of millions of dollars spent by the Devil's Brigade on developing bacteriological weapons, only two types, among hundreds tested, had any practical use. Porcelain "flea bombs," containing plague-ridden insects, were dropped on enemy troops, he said. In areas under the control of Communist leader Mao Tse-tung's Eighth Route Army, Tsuneishi said, salmonella germs were dumped into water supplies or injected into chocolate later distributed to Chinese children.

In 1944, Tsuneishi believes, the Japanese were prepared to deny the use of the airstrip on Saipan, their Pacific island stronghold, to invading U.S. forces by sprinkling it with plague-infected fleas.

The last-ditch stand failed, he says, when ships carrying the deadly cargo, and several hundred germ warfare specialists from Japanese "water supply" units throughout Asia, were sunk by American submarines before reaching the island.

Today in Harbin, where bitter memories of the Japanese occupation linger, Han said, "It is our point of view to distinguish between the Japanese people and the Japanese militarists. Most of the Japanese respect the history of this area. Some ignore it." A few, he added, "might even say no germ factory existed here, which we can never accept."