Because you can "prove" almost anything with a propaganda film, you can really prove nothing. That is one of the problems afflicting "Television's Vietnam -- The Real Story," a one-hour tirade put together by the Accuracy in Media (AIM) group to rebut the award-winning 1983 documentary "Vietnam: A Television History" and airing tonight at 9 on Channel 26 and other PBS stations.

The AIM film, narrated by the ridiculously pompous Charlton Heston, and produced, in part, on a foolhardy $30,000 grant from the National Endowment for the Humanities, is contained within a two-hour program, "Vietnam Op/Ed: An Inside Story Special." The decision to air the AIM film at all has brought cries of protest from within the journalistic community, if it can be called anything so orderly as a community, particularly from those who produced the original 13-part documentary.

By airing the AIM film, PBS seems to be expressing a lack of support for its own program and casting doubt on the credibility of those who made it. On the other hand, airing the AIM film may also give PBS the opportunity to defuse it. If it were not put on the air, the film might become something of an underground hot ticket, eagerly screened by groups already partial to its politically conservative approach, eagerly broadcast by local TV stations in conservative-minded pockets of the country.

Instead of letting the AIM film achieve David versus Goliath status as a cult item, PBS is going to let everyone see it at once. And that will let everyone know at once that there really isn't much to AIM's case, that the alleged grievances turn out to be very insubstantial, and that the film, divorced from its context of controversy, is in fact dull.

It is hard to see how any but the most passionately involved parties will be much provoked by AIM complaints about whether the PBS documentary identified Ho Chi Minh as a "nationalist" more times than it identified him as a "communist," or whether it was made absolutely, perfectly, crystalline clear precisely whom Ho killed or had killed in either 1925 or 1926, or whether sufficient time was given on the PBS documentary to a protest demonstration by those who supported, rather than condemned, the war when it was going on.

Is it really productive to continue the debate on whether the Tet offensive was a psychological defeat for the United States or instead merely a perceived psychological defeat?

A smattering of supposed experts, including a couple of silly congressmen and some disgruntled Vietnamese now living in the United States, are paraded by to dispute this or that point made in the original 13-part PBS series. Of them all, Rep. John McCain (R-Ariz.) seems more concerned with addressing a specific grievance than with summoning forth dark and sinister media conspiracy theories. He says, calmly and convincingly, that more attention should have been paid on the PBS documentary to the shameful way Hanoi treated American POWs. Footage of Jane Fonda prancing and grinning merrily through North Vietnam is justifiably inserted to embarrass the white-wine liberals who made protesting the war into sanctimonious exhibitionism at the time.

But none of this strikes at the heart of the original documentary's integrity or good intentions. It couldn't have been perfect, and wasn't, but AIM fails to support its charges that it was "flawed by serious errors and distortions," and that it turned the sorrowful story of the war into a "melodrama of heroes and villains."

The single most specious charge is made against the press in general, not the PBS show. AIM blames the media for the fact the war was lost. After giving examples of allegedly excessive media focus on war protest, Heston says, "This kind of distorted coverage had a cumulative effect on Congress. The results on the battlefield were disastrous." Even crackpots must wince a bit at this kind of assertion.

Broadcast journalists worry about the precedent PBS might establish with tonight's ignoble experiment. Offering a chance to make a reply is one thing -- ABC News does it, infrequently but earnestly, with the breakthrough "Viewpoint" programs -- but turning over the airwaves for an hour to propagandists who have produced their own movie is another. A ruckus in a similar vein erupted last summer when the Republicans wanted to show an 18-minute movie about President Reagan at their convention and insisted that the networks show it, too. At least that movie was well produced; tonight's AIM film is on the klutzy side.

In an attempt to save what is left of its tattered face, PBS surrounds the AIM film with extravagant annotation. First there is a long background piece on the original documentary, and some of those who made it are heard from (some others refused, understandably, to participate). After the AIM film is shown, a PBS-produced piece cites alleged inaccuracies in AIM's claims of alleged inaccuracies. Perhaps AIM will want NEH to cough up another 30 grand to produce a film to rebut the rebuttal of its rebuttal.

Finally, Harvard Law's dubious gift to television, Arthur Miller, conducts a discussion of the whole affair. Participants include AIM chairman Reed Irvine, who with or without his glasses comes across as a scowly TV cousin of David Letterman's famous frump Larry (Bud) Melman. On the subject of communism being treated in a news broadcast, Irvine asks rhetorically, "Is it something that we want a balanced picture of?" His complaints with the PBS documentary appear to be not that it was distorted, but that it wasn't distorted in ways he would find encouraging.

"Tonight you are in for some unusual television," Miller chirps at the beginning of the two-hour broadcast. Unusual, yes; edifying, no.