WHEN Earth Day finally arrives tomorrow, it will be the culmination of one of the biggest media events in recent memory. What began as an earnest attempt to enlighten the public about environmental issues has become a mammoth, multi-media publicity binge.

In the short-run, the hype surrounding Earth Day might do some good. The environmental movement, which once had a reputation for attracting only fringe liberals, has truly moved into the mainstream. Most Americans probably now know that styrofoam is bad and trees are good, that natural resources are not inexhaustable and that the garbage they put out on the curb is part and parcel of "the solid waste problem."

Unfortunately, for every dose of education there's a double dose of "ecomerchandising" trailing right behind. Of course, some products--such as mugs and recycled paper goods--are dedicated to the environment in function as well finance. And the recent barrage of "50 things you can do..." books have some valuable suggestions to offer, although their McEnvironment formats tend to trivialize the gravity of the problem.

And don't forget the Earth Day teeshirts, souvenir buttons and TV specials devoted more to personal profit than ecological edification. The many "celebrations" planned will no doubt feature vendors selling beer and coffee in non-recyclable cups.

That the Earth Day image has been hijacked by cheap merchandise does not in itself diminish the importance of Earth Day. But by treating the event as if it were the Super Bowl or Head of the Charles Weekend, its message is obscured, and support for environmental conservation is reduced to a mere fad. Earth Day now more resembles the Simpsons or Batman than a crucial consciousness-raising event.

When a "movement" becomes a "trend," it usually succumbs to the same fate as any popular fad--burn-out and eventual neglect. Recall Live Aid, the super-mega concert that graced everyone's TV screen five years ago. In the mid-1980s, caring about hunger suddenly became fashionable after some pop stars got together and made a few mushy records on the subject. By the summer of 1985, hunger-mania had reached epic proportions and the Live Aid concert was dubbed the event of the decade.

But the concert became an end unto itself, and when it was over, America went home. The hunger movement was never to be heard from again, as reports of poorly managed and squandered relief resources were largely ignored. "We had our fun," America thought, "We gave our token nod to hunger. Bring on the next hot movement!"

Earth Day seems to be proceeding along the same meteoric path. Judging from the publicity, the event is the celebratory culmination of an enormous conservation effort, after which we can all breathe easy and return to the status quo. This kind of complacency is what Earth Day should be rooting out.

Preserving the Earth requires a very conscious and sometimes difficult effort by every one of its inhabitants on a daily basis. It requires all people to fundamentally rethink the way they use material and energy resources.

The world cannot suffer from environmental burnout. We cannot think of Earth Day as an end unto itself--an "event"--because events come to an end. And the message that Earth Day brings must not come to an end.

If Earth Day is going to be anything more than a self-indulgent party/media event, every participant must consider its meaning on a personal level. If partying on the Charles will help you think about the sacrifices you are willing to make for the environment, then by all means go party. But the big party on the Charles won't save the environment. Instead of partying all day, try recycling your newspapers, taking shorter showers or going without paper cups in the dining hall.

Because when Earth Day ends, and Earth week passes, and the tee-shirts and balloons are gone, the Earth, with all of its scars, will still be here.