ITS NOT quite fashionable, yet, to be openly sympathetic to American servicemen who were convicted of murdering Vietnamese noncambatants, but it's getting there.

The rules of that war were all wrong, we're tempted to say. We couldn't fight guerrillas under the same rules we fought the Germans and the Japanese in World War II.

It's touchy, but a lot of Americans are bolder about supporting our presence in Vietnam, nowadays, and some who opposed it have had a few second thoughts about their moral condemnations.

Hence the popularity of the movie "Breaker Morant," in which the parallel with Vietnam at first seems obvious. Three Australian officers, fighting in the military and moral fog of the war against the Boer guerrillas in South Africa around the turn of the century, are convicted -- and two of them executed -- for wrongfully killing prisoners and a civilian. No matter that the difference between soldiers and civilians was impossible to tell, and no matter that they had orders to shoot prisoners, the movie says; Lord Kitchener has political motives for getting convictions and executions. He wants to demonstrate the good will of the British army.

The rules: the Australians had bee asked to fight a new kind of war under the old rules, just as Americans were asked to fight the Vietnam war under World War II rules. And in both cases, political pressure seemed to demand proof by the military that it had not gone savage with the strain.

"Vietnam came under a much greater microscope than any previous war," says James Webb, a highly decorated former Marine captain, and author of the Vietnam war novel "Fields of Fire." "The military wanted to show these incident [killings of noncombatants] were aberrations, while the anit-war movement was saying they were typical. The entire area was permeated with emotions from World War II," Webb says, citing the moral precedents established by the Nuremberg trials, which made a crime of the words "only following orders."

Seventy-one Americans were convicted of murdering Vietnamese noncombatants, according to Hays Parks, who is chief of international law for the Department of the Army and former prosecutor for the 1st Marine Division. One of the 71 was former marine Cpl. Stanley Luczko, who is written abut elsewhere on this page. He pled extenuating circumstances unknown in earlier wars: all Vietnamese were suspect, including women and children, and often, the enemy wasn't in uniform, making it hard to tell a guerrilla from a noncombatant until the moment he or she attacked.

The figure of 71 Americans convicted in a war of this order might seem alarming, and suggest political pressure to prove the morality of our forces through its willingness to court-martial wrongoders. Parks maintains, however, that "Vietnam was aobut the same as World War II and Korea." He is careful to differentiate between "Breaker Morant" and Vietnam. "I don't think we ever tolerated that kind of stuff, nor was there an order that came down authorizing the shooting of prisoners."

In fact, the prosecution of American troops in Vietnam seems mild when compared with World War II. Then, with no political pressure questioning the basic humanity of our troops, 141 Americans were executed -- not just convicted but executed - for murder and/or rape, according to a Judge Advocate General memo cited by government military historian Rod Engert. In World War I we executed 35 of our own troops, and in the Civil War, the Union Army executed 267. (In World War II, one other American was executed for desertion.)

This figure would make military judgment of Americans in Vietnam look lenient. It's important, however, to break down the World War II figure. Of those 141 executions, 35 were for murder of other Americans, and six were for rape of American nurses. The rest were for murder and/or rape of allied civilians, with only four executions for the rape of enemy civilians, and one for the murder and rape of someone in the category of "neutral and German civilians."

It would take a detailed search of a mountain of files to determine if these statistics meant that it was far more permissible to rape or murder enemy civilians than allied one, although the assumption is tempting. Nevertheless, in a war free of homefront moralists and protester, and of political pressure to demonstrate the good faith of the military, our justice appears to have been stern.

In Vietnam, however, it was not only hard to tell civilian from soldier, but the allies and the enemy were all countrymen.

"It was a completely different war in Vietnam," says Robert Zsalman, of the Board of Correction of Naval Records. He cites the fact that not only could the enemy be women or children, but guerrillas didn't wear uniforms."

The Army's Hays Parks says: "Most of the incidents in World War II were with rear-echelon troops," which separates them at least from cases such as that of Cpl. Luczko, who was on patrol, or, in the extreme example, Lt. Calley.

In any case, the statistics make uncertain the "Breaker Morant" parallel with Vietnam. But maybe it takes just such a movie to enable us to examine the case of Cpl. Luczko and other dilemmas of Vietnam in goo faith -- that is to say with the courage to accept the necessity of moral, military and factual ambiguities, a courage which too many Americans lacked during the war itself.