FEAR AND fascination have always marked relations between man and shark. Hefty helpings of both are to be had in the National Museum of Natural History's new shark show.

There's no particular reason for the show except, perhaps, that the subject is very close to the heart of museum director Frank Talbot. As a young man in Australia, Talbot had a radical mastectomy performed on him by a shark to whom he had shown too little respect.

Talbot laughs about it now. "Of all the parts he could have bitten off, I miss the breast least," he says. Actually, Talbot laughed about it then, along with the mate who was pouring iodine into the wound. "Had to laugh or cry," he says.

Visitors will experience similar mixed emotions in the exhibit, which alternates between the beauty and deadliness of sharks, their wonderful efficiency and the awful anxiety they inspire, and our use and abuse of them.

We eat an awful lot more of them than they do of us, and also make soap, cosmetics and margarine from their carcasses. During World War II the Japanese used super-slippery, non-freezing shark oil in aircraft engines. Sharkskin is used for shoes and sandpaper. And if Talbot should survive another shark attack, the beast's own cartilage may be used to supplement the skin grafts.

Imported from the Natural History Museum of Los Angeles County, the show is heavily spiced with Gary Larson's "Far Side" cartoons and shark factoids:

Bull sharks are the most dangerous, and are equally at home in fresh water; they swim up the Mississippi as far as East St. Louis.

Lemon sharks rival rabbits in their ability to run mazes.

Sharks can detect one drop of blood in a million molecules of water.

Cookiecutter sharks nip biscuit-sized chunks out of whales, dolphins and nuclear submarines.

Patrons enter a pathway, blue-lighted to suggest the ocean depths, that threads among 17 life-size shark models. If that doesn't send you screaming out of the museum, you're invited to compare your bulk to that of various sharks (your correspondent's as heavy as a bull shark and as long as a hammerhead).

The show is inescapably schizoid. On the one hand we have Merlin Olsen narrating a bathetic film that pleads for appreciation of sharks, and on the other we have a display case full of things that have been taken from the tummies of tiger sharks: hubcaps, a windlass, a bomb, a bronze propeller, a bongo drum, a pair of sneakers, a mink coat, a license plate, lumps of bunker coal and a suit of Spanish armor, sans conquistador.

Love 'em or loath 'em, sharks have ruled the seas for 400 million years. They have seen the rise and fall of the dinosaurs and, so far, the rise of mankind.

SHARKS: FACT AND FANCY -- Through Jan. 20 at the National Museum of Natural History, 12th and Constitution NW. Open 10 to 5:30 daily. Metro: Smithsonian.