ABC examines the use of chemical and biological weapons in Asia in an effective documentary in the "Close-up" series, called "Rain of Terror," tonight at 8 on Channel 7.

The issue is warfare by toxic clouds. What has been in the news for three months is the charge that the Soviets themselves or their allies have freely carried on this outlawed kind of war for years.

Now the gray newsprint becomes vivid images: blistered bodies, silent corpses, wounded refugees describing their pain. There are even two defectors telling how they helped release the red, yellow and black clouds of death in the jungle.

It is a difficult subject because of the wars that continue in the jungle, because of the different cultures and languages involved, because most of the evidence is taken from stories told by refugees. These are confirmed by a few scraps of military intelligence, and finally, very recently, by samples of the agents believed to be used.

The reports of chemical warfare extend back as far as the early 1960s and the Yemen civil war. But the best evidence is from the six years of reports coming from Laos and Cambodia, reports that describe gas warfare attacks against the Hmong hill people of Laos.

For its documentary, ABC has come up with its own sample of the substance used in Laos against the Hmong people.

We see pictures of the Hmong who brought the sample out, and Charles Whitney, the operator of a clinic who received the sample and held onto it for about five months, unsure just what to do with it.

ABC took the sample, sent it out for analysis and found pretty much what the State Department has found in its few samples -- the presence of poisons that are called mycotoxins. The analysis also found a chemical that is used in aerosols, in this case presumably to make the cloud in which the other chemicals are carried.

There has been some question whether the mycotoxins in the State Department samples simply grew naturally on the plants in Asia. But the aerosol found in ABC's sample is only a man-made substance, one unlikely to have found its way into the jungle naturally.

There has been some doubt whether mycotoxins can cause the exact symptoms described by refugees, particularly the bleeding. ABC shows us the death of a pig that has been fed a mycotoxin. We see the vomiting, the convulsions, and later the bloody, hemorrhaged stomach wall. The symptoms fit.

We see other things, including what appears to be gas attacks by Soviet helicopters in Afghanistan.

There are still loose ends in the story that are unlikely to be answered by one documentary or 20. The first is why the Soviets, if it is the Soviets, would carry out this kind of warfare? Don't they fear detection? Why use these unusual and new agents of warfare rather than the more familiar and more deadly nerve gas?

And there is the question that the ABC documentary concludes with: If the evidence is now so good, why has the United States not pressed harder to save the Hmong people and to stop this gross violation, this kind of war we thought was prohibited?