On Earth Day, 1970, a shop opened in New York to sell “Earth Shoes,” fan-toed clodhoppers with heels lower than their toes. The shoes are ugly as sin but supposedly promote a healthier, more comfortable posture than normal shoes. Fad or philosophy, Earth Shoes are the hottest footgear around and are selling out at 53 stores across the country.

The Earth Shoe factory in Midleborough, Mass., has quadrupled its staff to 200 in the past year, and has quadrupled its production to 250,000 pairs for this year. But the company’s headquarters in New York still is behind on mail orders by 3,500 pairs. The Earth Shoe store in Washington D.C., is doing so well that it hasn’t had to advertise in six months. The store in the Westwood section of Los Angeles - which caters to such Hollywood heavies as Sidney Poitier, Bob Dylan, and Peter Fonda - has changed its telephone number four times in the last year to escape a flood of inquiries. “People are hip to our shipment schedule,” said shop manager Jim Irrer, “and word spreads so fast when the shoes arrive that the store becomes a madhouse.”

Earth Shoes come in four models (boots, oxfords, sandals, and sling backs) costing between $23.50 and $42.50. The shoe is so popular that other manufacturers, including Florsheim, are now selling imitations.

Tippy: The originals were invented in 1957 by Anne Kalso, now 69, a Danish costume designer, yoga expert, and healthy buff. She had noticed that footprints on the beaches showed the heel sinking deeper than the toes. Subsequently she designed a shoe with the heel half an inch lower than the ball of the foot, to promote a straighter spine and improve breathing and circulation. Some podiatrists endorse the shoe, but they - and Kalso herself - warn that Earth Shoes can be harmful to people with flat feet or Achilles’ tendon problems. The shoes can also be tricky to get sued to. “It’s funny to watch people stand in them for the first time,” says Artie Aaron, manager of the New York store. “One lady leaned so far backwards I had to catch her.”