Twenty years ago my parents took me to Mackinac Island up where Lake Huron meets Lake Michigan. Cars aren't allowed there for transportation. You can only get around by foot, bicycle or horse. Since the gas crunch is about to make the rest of America a national Mackinac Island, it's worth looking at what that could mean.

First, kiss Turtle Wax good-bye. Twenty years hence, children rummaging in the basement may find an old crusted green bottle of the stuff and figure that while it was nice their parents worried about endangered species, waxing reptiles may have been a bit much.

Homebound Americans will be desperate for a hamburger fix and a reconstructed Ronald MacDonald will become the Harry Truman of the year 2000. Count on Trailways and Greyhound to offer summer excursion rates to Roy Rogers resorts where, in true Williamsburg fashion, visitors will view the vanishing art of fast-food preparation. Tours will be followed by a feast of fries, malts and burgers made from the finest beef, blimp-lifted from Argentina.

State departments of motor vehicles might still exist but they won't be issuing driver's licenses. Instead, they'll provide walk, stroll and jog permits. Levies will be imposed according to shoe size with the minimum rate for flip-flops and the highest tax for Dr. Scholl-guzzling wing tips. People above the age of seven will be forbidden to go barefoot.

Life insurance rates will soar to replace revenues lost from the sale of automobile insurance.

Bet on the housing industry to profit from a new boom in garage sales. Garages, renovated into efficiencies or 1-bedrooms, will be available for $65,000 with 30 percent down.

After a century's-end decline, the house plant craze storms back. American Motors' Gremlins, inserted vertically, windshield-deep in the front lawn will be the most prized flower pots. Those rare beasts, the hulking 1959 Oldsmobile station wagons will become coveted gazebos replacing ducks, deer, plastic geese and little cast iron jockeys as the most popular lawn decoration.

Don't be surprised if the Book-of-the-Month Club markets volumes on the breaking of the auto industry the way they sell books today on the end of the Third Reich. Titles will include, "Earl Shieb: Broken Patriot" for $39.95 and "The Midas Touch." A supplementary selection will tell the tale of an enterprising precinct committee woman in Duluth, Minn., who made a fortune replacing the bumper sticker with the forehead decal.

Look forward to the C&O barge canal becoming an important means of commuter travel in the East. Offenses against mules will carry with them a minimum 2-year sentence. I-66 will be to the Washington of the year 2000 wha.t the C&O canal was to the Washington of 1950.

One change hitting sportswriters directly in the expense account will be the disbanding of the NBA, the NFL and the major leagues. Without fuel to get to the ballparks, canasta will become America's number 1 sport. State governments will impose a $12 excise tax on playing cards, which will be sold in computer-coded cases. Each time the case is opened, a users fee of $2.50 will register in a central computer with bills sent quarterly.

Expect changes in zoning laws. Parking lots will be dug up, sodded and rezoned for Guernsey and Holstein. Livestock will take care of both cutting lawns and keeping them green while shepherds will drive goat herds through the neighborhoods in lieu of weekly garbage collections.

Of course it's easy to snicker at a fate you really can't believe will come. The human hardship in the wake of an automobile industry decline would be devastating. Besides, I don't really remember whether I even liked Mackinac Island. To tell you the truth, the best part was the drive up there.