WHEN Earth Day was first celebrated 20 years ago, few people other than hard-core liberal activists and tree-hugging environmentalists took part. Today, in the wake of high-profile environmental disasters and increasing media coverage of environmental issues, preserving the environment has become a hot issue du jour. Even George Bush, as a Republican presidential candidate, made rhetorical commitments to conservation and environmental clean-up.

Before the hoopla subsides, Harvard students and other citizens of the earth should consider the message of Earth Day (April 26) and Earth Week (April 20-27): prosperity at the expense of posterity is no bargain. The crass commercialization of this year's Earth Day events does not detract from the importance of this message.

Although preserving the environment is an issue that cuts across the political spectrum, liberals have traditionally carried the bulk of the weight in the struggle. Indeed, the message of Earth Week is best captured by the popular liberal bumper-sticker, "Think globally, act locally." This week's lectures and discussions about the policy choices involved in environmental conservation offer a global perspective, while the events promoting conservation and recycling teach simple, affirmative steps that individuals can take to do their part.

If nothing else, students should celebrate Earth Day by vowing to forego paper cups in the dining halls in favor of reusable glasses and mugs. Students should also do without plastic shopping bags and should use the recycling bins in their entryways to recycle newspapers, white paper, glass bottles and aluminum cans.

The value of these individual actions is abundantly clear. Making newsprint from recycled newspapers uses half the water and energy and causes 74 percent less air pollution than making it from pulp wood. Making glass from recycled bottles reduces energy consumption by nearly half, water consumption by half, air pollution by 20 percent and mining wastes by 80 percent.

AMERICANS have traditionally been willing to do anything to protect the environment--anything, that is, that does not involve the slightest inconvenience to themselves. Even after Earth Week is over, it is important to remember that the daily choices we make as consumers and citizens can help or hinder efforts to bequeath a habitable planet to our children.

Earth week is a time to consider the small, individual sacrifices that we can make to sustain and improve the quality of life on our planet. Every Day is Earth Day, which bills itself as "the official New England Earth Day 1990 action guide," is chock full of such suggestions. And though some of them--such as using cloth diapers and not eating meat--are of questionable value, the importance of the idea of individual sacrifice cannot be overstated.

In the words of another liberal bumper-sticker, we must "live simply, so that others may simply live."