Before modern zoology got to work and ruined everything, it was common knowledge that the giant squid rose out of the sea and with horrible tentacles snapped the masts of ships and gobbled up sailors.

But if you go to the National Museum of Natural History today (or hereafter) you may see the ferocious monster in a little coffin, floating in 75 percent alcohol (it's one big martini, a spokesman observed) and it's a pretty sorry sailor indeed that would be afraid of this beast.

He washed up on a Massachusetts shore in 1980 and was borne on a stretcher off the beach. He was already dead, as giant squids always are when you find them on a beach, and was shown for a time in Boston before coming here. Where Dr. Clyde F.E. Roper is on fire to dissect him, but will wait a year or so in order for us all to peer over the edge at this innocent monster.

In life, he was a splendid rosy maroon (the color now abraded by the sand) and measured about 30 feet from his tail to the tip of his feeding filaments. The largest giant squid ever measured was 60 feet long, so this specimen is medium-sized.

But exquisitely rare.

"They have a papier-ma che' model in [the American Museum of Natural History in] New York," said Roper, who added there is no other museum where you can see a genuine-stuff squid. They live at perhaps 300 feet beneath the sea, or perhaps 12,000 feet (virtually nothing is truly known about their habitat) and while a dead squid occasionally washes up on shore, even that is rare.

For all its impressive 30-foot length, the main bulk of the creature is amply housed in the 9-foot alcoholic coffin, and, before some of him wore away in the weather, he weighed perhaps 400 pounds. Most of the length came from two vastly prolonged tentacles, at the end of which he caught small fishes.

These feeding filaments were lost, and you have something no greater in bulk than a Mississippi River catfish. Which is impressive enough.

Squids are descendants of primitive mollusks, the shell now gone, and substituted for by an interior translucent skeletal rod from fore to aft--all that now remains of the original primitive internal calcareous shell.

The main enemy of the giant squid seems to be the sperm whale. The whale's precious ambergris, the superb fixative for expensive perfumes, is thought to be primarily an oily means by which the whale flushes out indigestible parts of the giant squids he has eaten.

The squid's eyes are the largest known in nature, about 10 inches across or somewhat larger than an automobile headlight.

It is thought the giant squid does not have a home to which he returns every night, but that he floats about not far off the rocks of a continental shelf or other inaccessible place. The shortage of squids caught in nets is presumably due to their rocky homes, which fishers do not bother for fear their nets will be damaged.

The giant squid, unlike some others of the family, is thought to be a moderate swimmer, not one of those superlative swimmers. Since no giant squid has been kept in captivity, so far as is known, not much is known of the creature's habits. Roper suspects he has "periods of quiescence, instead of sleep; he certainly does not curl up with his head on a pillow," but is rocked in the cradle of the deep, as it were.

The great squid is intelligent, Roper swears, without adducing much evidence, admittedly, since there may not be much. One gets a feel for these things, however, and the squid in the box certainly looked far more intelligent than your average oyster.

The animal's overlapping mantle is fitted with a ridge of cartilage that can be fitted against a similar ridge at the base of a funnel, and when properly hooked up the squid forces all the water collected between the mantle and the head through this funnel, thus achieving excellent mobility and speed. The funnel, analagous to the foot of a mollusk, can be turned various ways to control direction, and is fitted with a flap serving as a valve to keep sea water from running back in.

A female squid may have a million eggs in one mass. They are fertilized, it is thought, when leaving the oviduct by a little cylinder containing sperm, which the male attaches to the female's body. The sperm-bearing capsule has a triggering device somewhat like a hand grenade.

Such a heavy animal need not spend great energy swimming, in order to keep from sinking, since the muscles have high concentrations of ammonium ions, which have a slightly lower specific gravity than sea water. The rest of the body is heavier than seawater, so things even out and the squid requires little energy to stay at any one level, neither rising nor sinking.

If a sperm whale attacks such a squid, the squid fights for life though he is no match for the whale, and tries chiefly to escape. Whales are found with scars made by the squid's many suction cups along his arms. By measuring the size of these suction-cup scars on whales, incredible lengths were sometimes computed for squids, since the larger the squid, the larger its cups. But then it was remembered the whale's scars increased in size as the whale grew. A fairly small suction cup may have made the original scar.

The great squid occupies the genus Architeuthis alone, and those who study cephalopods (which include also the octopus and the cuttlefish) are called Teuthologists. One rarely runs into them. They occasionally write splendid articles on squids for Scientific American, however, as Roper and his friend Kenneth J. Boss did.

Roper, who as the Smithsonian's expert on squids is naturally very far gone on them, finds the natural facts of the squid more wonderful than all the old sailor-lore about squids as sea monsters. It is all nonsense that squids snapped masts and gobbled sailors. Of course, he went on, if a little boat ran into a giant squid quietly expiring on the sea surface and tried to catch it, the squid might "rear up to protect itself, gripping the boat with its arms and tentacles."

In other words, there's hope yet.