For several weeks now, news media have provided sensational reports on grisly nuclear experiments by the U.S. government - secret tests such as injections of plutonium and X-rays of the testicles of prison inmates.

Few stories, however, have shed light on a key truth: Ever since the dawn of the Atomic Age a half-century ago, nuclear activities have involved large-scale experimentation on human beings without their voluntary or informed consent.

In August 1945, the U.S. government selected Hiroshima and Nagasaki as ideal sites for measuring the effects of atomic weaponry. Hundreds of thousands of civilians died in those Japanese cities - which were large enough to show the gradations of what a nuclear explosion could do to buildings . . . and human beings.

The director of the Manhattan Project, Leslie R. Groves, later recalled that it was "desirable that the first target be of such size that the damage would be confined within it, so that we could more definitely determine the power of the bomb."

During the next 17 years, hundreds of U.S. atmospheric bomb tests - in the South Pacific and at the Nevada Test Site - exposed millions of people to intense nuclear fallout . . . without their informed consent. Cancer, leukemia and other horrendous effects, including genetic injury, were widespread.

In the Marshall Islands and elsewhere in the Pacific, many native people suffered. So did large numbers of downwind residents in Utah, Nevada and Northern Arizona, plus many of the 300,000 U.S. troops who were exposed to nuclear detonations at close range.

Test site workers suffered similar effects. So did many Native Americans - hired to mine uranium and sent into what amounted to radon ovens.

Survivors have been left to grieve in silence. As one downwinder in Southern Utah told us, speaking of government officials: "We bury the dead; they don't."

There have always been a few gutsy journalists struggling to pull the public-relations mask off of nuclear realities - even during the height of the Cold War.

Nearly 40 years ago, investigative reporter Paul Jacobs did research in the vicinity of the Southern Nevada desert, where mushroom clouds from nuclear blasts rose on a regular basis.

While the big media of the day stuck to the government's nuclear line, Jacobs - on a shoestring budget - wrote an exceptional in-depth article titled "Clouds from Nevada." Appearing in The Reporter magazine in 1957, his article challenged the safety of open-air nuclear tests. It was prophetic journalism that - if heeded at the time - would have prevented a great deal of fallout-induced harm yet to come.

Two decades later, while at work on a documentary film updating the story, Jacobs died of cancer. His associates completed the movie, titled "Paul Jacobs and the Nuclear Gang," chronicling life and death downwind of the test site.

The documentary won the only Emmy award that PBS received in 1979. But many TV viewers didn't have a chance to see it. Under pressure from big-money nuclear groups such as the Atomic Industrial Forum, nine of the public TV stations in the nation's 24 biggest areas refused to air the film.

Many of the types of experiments making front-page news these days were documented long ago. In 1986, Rep. Edward J. Markey released a congressional report titled "American Nuclear Guinea Pigs: Three Decades of Radioactive Experiments on U.S. Citizens." But the report got little publicity, in part because of media deference to the Reagan White House.

As Markey recounted a few weeks ago, "There was a massive public-relations partnership that existed between the administration, the defense contractors and experimenters in America that worked very effectively throughout the 1980s. I'd say something, and I'd get attacked, and it would be a one-day story."

Today, the twin nuclear enterprises of arms production and power plants continue to produce big corporate profits - and massive amounts of radioactive waste.

People living downwind and downriver of nuclear facilities - from Hanford in Washington state to Savannah River in South Carolina - continue to be "guinea pigs."

As the federal government moves to re-tool its nuclear weapons assembly line, plans include the development of "micro-nukes" and "mini-nukes," along with scenarios for "recycling" plutonium and producing tritium for future bombs.

The recent news coverage of horrible experiments, inflicted in past decades on several thousand people, tends to obscure a crucial present-day reality: The entire nuclear cycle - from uranium mining to reactors to atomic waste - remains a mass "nuclear experiment" on us all.