The knock against the news business, one more popular than ever with the Reagan administration, is that it never tells the good news about Our Side or the bad news about the bad people on The Other Side. There's an answer, having to do with human nature and accessibility and even human frailty, but never mind. If that's how you feel about it, here is a two-fer.

The bad news is a recent report on the awful vengeance visited by the communist conquerers on the vanquished of South Vietnam--the unrelievedly grim record of the Socialist Republic of Vietnam on human rights in the eight years since the Saigon government was crushed by North Vietnamese tanks in April 1975. The report is amply documented from official SRV statements, eyewitness reports from visitors and refugee accounts. It was assembled by the Aurora Foundation of Atherton, Calif., a nonprofit organization dedicated to "improvement in the observance of human rights throughout the world."

You could say this isn't so much news as a pulling together of bits and pieces of earlier reports, including those of the most celebrated international, private investigator of human rights violators: Amnesty International. But like a lot of other Vietnam legacies, the pieces tend to get shuffled out of sight. Those who opposed the war effort are uncomfortable with the we-told-you-so's of those who warned of the worst if the war was lost. The latter have no easy answer to the question of how it might have been won.

So the hard evidence makes for hard reading, whatever side of the original argument you come from. There is no blinking at the Aurora study's finding of religious prosecution, repression of ethnic Chinese, and the brutal "reeducation program" inflicted upon "war criminals" for their roles in the army or the government of what was South Vietnam--the beatings, starvation, and cruel punishment in underground "tiger cages" or metal freight containers.

And what makes it all the harder is that there doesn't seem to be a whole lot that anybody can do about it.

What, then, is the good news? It is this: that there exist here and around the world hundreds of high-minded, hardheaded people who refuse to give up hope; that there is an Amnesty International, whose apolitical faith in the power of disclosure has brought about the release of thousands of political prisoners; that there are smaller groups with the energy and dedication to assemble an Aurora Foundation and--to reduce generalities to a particular --that there is a Ginetta Sagan, who helped organize Amnesty International, serves as the executive director of The Aurora Foundation, and is co-author of the report on Vietnam.

Sagan got into the human-rights cause, first, by being a victim. A fighter in the Italian Resistance, she lost both her parents to the Gestapo. She was arrested in the mountains of northern Italy in the winter of 1945 and tortured horribly before being forced to write her own death sentence. She was saved by the arrival of Allied liberation forces a few days before she was to be executed.

I first met her in the late '60s, when she was deeply involved with Amnesty. Not the least of her anguish was directed at the "tiger cages" holding political victims of South Vietnam's government. That would make her, in the conventional shorthand, anti-Vietnam War.

But what distinguishes her and her kind (including a close co-worker, the folk singer Joan Baez) is the single- minded universality of their approach to the plight of "prisoners of conscience." They have no ideological hangups in their leap to the side of today's "prisoners of conscience" in Vietnam.

Sagan is as tough-minded as she is compassionate, bright-spirited and witty. She can laugh at the idea that old colleagues from the far left in the Vietnam War days now accuse her of having switched sides. But she sees nothing funny about the "selectivity" involved in opposition to communist violations of human rights--but a blind eye to those committed in South Africa, Argentina or Pinochet's Chile.

The international private eyes know they can do little more, by themselves, than uncover human rights violations; they cannot break down prison gates. But the Ginetta Sagans of the world also know that they can sometimes unloose enough public outrage to move governments in ways that can turn the keys.