THE FRENCH press, this fall, has repaorted an unusual number of cases of mushroom poisoning, at least one fatal, that of a child. Children, understandably, sometimes succumb to toxic doses smaller than those which adults could resist. It may be that this exceptionally high incidence of mushroom posioning is linked to the unusually bad weather visited this year upon France: The concentration of toxins in mushrooms can vary greatly with local or temporary conditions. Normally, the danger of dying from mushroom poisoning should not be much greater than that of being killed by lightning; but rare though such accidents may be, some persons each year are struck by lightning and some persons do die from eating poisonous mushrooms. If the fear of mushroom poisoning is out of proportion to the danger, it is nevertheless shared by many whose opinions cannot easily be shrugged off as mere superstition.

"I admit," wrote Alexander Dumas, "that nothing frightens me so much as the appearance of mushrooms on the table, especially if I come upon them by chance in some small provincial town. Many are poisonous and even the good ones may poison to a mild degree those who, like the Emperor Claudius or the Trimalchio of Petronius, are tempted to over-indulge." This is not the most potent argument Dumas ever formulated, for the case of Trimalchio, a figure of fiction, cannot be taken into consideration by this court, which cannot agree either that Claudius was poisoned only "to a mild degree," since he took the liberty of dying when his wife, Agrippina, who thought it time for her son, Nero, to ascend the throne, fed him a mess of venomous mushrooms.

"There are as many varieties of poisonous mushrooms as of edible ones," wrote the late Rosie Maurel in her "Dictionnaire des Aliments." F she meant by this that 50 percent of mushrooms are poisonous, she was wrong by at least 48 percent. Only 1 to 2 percent of mushrooms are poisonous, which does not mean mortal; only about a dozen are fatal. The French manual of Habersaat and Gallant recognizes 15 which cause considerable commotion in the digestive system, but do no permanent damage, 10 which do harm the nervous system with lasting effects; and five which may cause death. The Italian mushroom encyclopedia of Augusto Rinaldi and Vassili Tyndalo names 10 whose evil effects are limited to the digestion, of which one is on rare occasions fatal; six which are harmful to the nervous system, none of them mortal; and eight which can cause death -- but of one, Gyromitra esculenta, whose very name proclaims edibility, it expresses reservations on its own verdict: "Once dried, this mushroom is completely harmless; but when it is fresh it is not well tolerated by everybody, especially if it is only slightly cooked, consumed with the water in which it has been cooked and eaten in large quantity. For some people, it is particularly harmful when eaten in successive meals. But over the years it has been sold in many markets and consumed without harm by many persons."

Habersaat and Gallant are less inclined to give Gyromitra esculenta the benefit of the doubt. They write that it contains two poisons, "helvellic acid, which dissolves in hot water without losing its toxicity, but, however, volatilizes on drying, and another poison still unknown which acts on the nervous system."

Another French authority writes that there are only five mushrooms capable of causing death -- Cortinarius orellanus, Lepiota helveola, Amanita verna, Amanita virosa and Amanita phalloides. Everybody agrees that the last is the deadliest of all mushrooms, one whose ingestion comes very close to meaning certain death: it accounts for 90 percent (some even estimate 95 percent) of all deaths from mushroom poisoning. This mushroom has gained such a horrendous reputation that some manuals warn that it should not even be touched, something of an exaggeration. Experienced mushroom gatherers have been known to help themselves identify it by biting off a small piece to sample the taste; but they spit it out immediately, swallowing nothing. I do not recommend this practice to neophytes.

Despite the terror which Amanita phalloides, the deadly Amanita, has imposed upon mushroom eaters, we are clearly very far from being ambushed by as many poisonous mushrooms as edible ones. About 2,000 are eaten currently in one part of the world or another. In short, you could browse among mushrooms at random and the chances of death, or even of serious intoxication, would be slight, statistically speaking. However, nobody wants to be a statistic on the wrong side of such a situation, even with the honor of being a rare statistic, so you had better be careful.

It cannot be asserted that the effort to educate laymen to avoid dangerous mushrooms has always been exerted with a maximum of intelligence. Mycologists renamed the deadly Amanita the Death Cup in this century and its hardly less toxic cousin Amanita virosa the Angel of Death, in the laudable intention of warning amateur mushroom hunters away from them.

Names are not a sure sign of a mushroom's nature in any case. Satan's boletus, a villainous red, looks poisonous and it is (but it is not mortal); however the Trumpet of Death, Craterellus cornucopioides looks poisonous too, but it is not. It lives up to its name by being of a cadaverously pallid purple, but it is so good that French sausage makers put small bits of it into trheir ware hoping that the customers will take them for pieces of truffles. One Parisian restaurant, perhaps in a spirit of bravado, has made a sort of trademark of this mushroom, carrying its ominous name on the menu all year around, serving it fresh in season and dried the rest of the time.

One of the reasons why Amanita phalloides is so dangerous is that it looks so innocent. "The problem with Amanita phalloides," according to Dr. Raymond Sarda, a mycologist himself, who treats mushroom poisoning at the Fernand Widal hospital of Paris, "is that it's extremely beautiful, very tasty, and closely resembles several of the edible mushrooms. In fact, the most beautiful Amanitas -- those that are young and fresh -- are the most poisonous because their concentration of poison is higher." Amanita phalloides can easily be mistaken for the edible Russula virescens, the likewise edible Tricholoma portentosum (the pretentious tricholoma), or even for its close relative, the common blameless meadow mushroom, Agaricus campestris. It has a healthy appetizing aspect, a pleasing odor which suggests clover hay when young, does not change color or exude latex when cut or broken, and is of a mild and pleasant flavor according to witnesses who are no longer with us. One and a half ounces of this seductive mushroom is a lethal dose according to one authority, but another puts it at 20 grams, which is only seven-tenths of an ounce.

Amanita is the most villianous genus of mushrooms. Not only does it include the deadliest mushroom of all, but also two others capable of causing death, Amanita virosa and Amanita verna, one which falls just below the deadly level, Amanita muscaria; and several which are toxic in various degrees short of fatality. However, there are more than a hundred species of Amanita, many of which are edible, notably one which everybody lists among the world's best, Amanita caesarea, Caesar's mushroom, so named because it was the one the Emperor Claudius was eating when Agrippina enriched the dish with a few Amanita phalloides, making Nero emperor in short order.

Most toxic mushrooms provoke a reaction in an hour and a half to two hours after eating, but Amanita phalloides produces no symptoms of poisoning until after its toxin has entered the blood stream, too late to use a stomach pump. This means from eight hours to as long as 48 hours after eating, so that the unsuspecting victim has sometimes enjoyed a second meal of deadly Amanitas before he realizes what has happened to him. Death usually follows in two to four days.

After the mortal Amanitas, the most deadly mushroom appears to be Cortinarius orellanus, which may have caused more deaths than have been attributed to it, for it is difficult to be sure whether or not it is this mushroom which has been the source of an intoxication, for the first symptoms of its poisoning may not appear until a fortnight after it has been eaten. The other members of this genus are generally edible, or at least harmless, except for Cortinarius cinnamomeus, which is labeled "suspect": the coroner's verdict is not yet in. Four others which resemble it are better avoided, though their cases are not clear.

From this point onward, the toxicity of mushrooms follows a descending scale. Some of them may cause discomfort, but they will do no lasting damage; and a large percentage of those which are toxic protect you from eating them by forbidding odors or tastes.

Your chances of contracting mushroom poisoning are apparently less in America than in Europe, but not much less. Europeans once thought that Amanita phalloides did not exist in the United States because there were so few deaths from mushroom poisoning here as compared with the toll in Europe. But this may have been only the result of the disinclination of Americans to eat wild mushrooms at all. When collecting them began to be a hobby, America chalked up its quota of mushroom poisoning deaths too. The United States is endowed with Amanita phalloides, which, indeed, seems to be found almost everywhere in the world except Africa and, in Europe, on the Iberian peninsula.

The United States not only has its full share of Amanitas, it also has the suspect Cortinarius cinnamomeus (but perhaps not the deadly Cortinarius orellanus). It knows also the debatable Gyromitra esculenta, sometimes called the false morel, since it resembles, though not very closely, this delectable mushroom. So far as I know, it does not have Lepitoa helveola.

You can always protect yourself against mushroom poisoning by a method which Dr. Raymond Sara asserts has actually been employed in Europe, not, one hopes, on a large scale. "There have been cases," he told an interviewer in l972, "when people gave their friends mushrooms without eating any themselves, waiting to see whether their friends would be well the next day." Friendship can go no farther.