A documentary by David Zeiger. Featuring Jane Fonda, Donald Sutherland, and Donald Duncan. Rated 14A. Opens Friday, July 21, at the Ridge

Now that American networks cannot be relied upon for anything like news, most viewers have to get their dope from comedy shows and documentaries. Just recently, we've seen effective contemplations of global warming and environmental rape for short-term profit (An Inconvenient Truth and Who Killed the Electric Car?) and docudramas about the so-called War on Terror (The Road to Guantíƒ ¡namo).

Few commercially released docs delve into the rapidly receding past, however. Yet the subject of Sir! No Sir! has much more relevance than might initially appear evident. It doesn't take great exposure to this expertly assembled film to recognize the parallels between America's disastrous adventure in Vietnam and its current Iraq debacle.

Rather than giving background to the war, or even the movement to end it, writer-director David Zeiger (best known for documenting high-school life in Senior Year, a superb reality series shown on PBS four years ago) throws us into the thick of things toward the end of the futile conflict. Mostly, we meet an assortment of compelling characters””in then-and-now footage””including Donald Duncan, a Green Beret who balked when the treatment of Vietnamese “went against everything I had been taught” ; Howard Levy, a doctor who refused to train men going overseas when he realized they would be brutalizing civilians; and Susan Schnall, a nurse who returned from Nam to help drop antiwar leaflets from a hired plane.

Other ex-soldiers recall life in San Francisco's overstuffed Presidio stockade, where the sign over the gate (“Obedience to the Law is Freedom” ) still brings to mind a certain famous camp in Poland. Dramatic highlights include the riot that followed the murder there of a mentally disturbed prisoner. One convict, Keith Mather, escaped to Canada, where he spent almost two decades. Another officer, Louis Font, became the first West Point grad to refuse to fight in a war.

These oral histories are varied and compelling, especially when juxtaposed with well-chosen snippets of archival images and supported by just the right period music. But a couple of points stand out in their refutation of right-wing memes that have subsequently obscured the experiences of the vets themselves. First off, it turns out that Hanoi Jane Fonda (son Troy Garity narrates) performed for thousands of wildly cheering GIs at the height of the war; and even more crucially, this companion to the overlooked Winter Soldier doc suggests that the era- characterizing moment when vets returned to be spat upon and called “baby killers”  is actually a myth propagated by right-wingers in order to discredit the activist movement.

I'm not sure if Sir! No Sir! could change the minds of viewers determined to leave authority unquestioned. But then as now, if they really want to support the troops, perhaps they could stop yammering and listen to them for a change.