Grenada is no longer on the front pages. But it was only two months ago that the United States invaded the Caribbean island, purportedly to prevent its slipping into anarchy. There remain unanswered questions about the action. But the Reagan administration has lived up to its early promise to remove most of the invading soldiers and marines.
Now comes the more difficult task: helping Grenada's 110,000 citizens build a viable, democratic society for their nutmeg- and clove-producing island. Ultimately, the responsibility for this task rests with the Grenadians themselves. But they need help. Grenada's sister islands in the Caribbean - led by Barbados, Dominica, and Jamaica - should exert a dominant influence in the effort. Since they called on the US to help in ousting the Marxist extremists who had taken control of Grenada, they share responsibility for the US-led invasion.
The US, however, has a continuing role to play also. Grenadians generally appreciate the US action. Many, agreeing with President Reagan, prefer calling the invasion a ''rescue mission.'' But with US troops largely gone and other pressing foreign and domestic issues dominating thinking in Washington, there is danger that Grenada could get lost in the shuffle. This must not happen. The US has already provided several million dollars worth of humanitarian aid to the island in the wake of the invasion. It has also helped Grenada nutmeg producers find a market for 1.1 million tons of the spice originally destined for the Soviet Union before the invasion.
But with the new year, Washington needs to appreciate the opportunity it has to quietly provide Grenada with relatively inexpensive assistance. Grenada, for example, has asked the US to send Peace Corps volunteers ''as soon as possible'' to rebuild agricultural, health, and educational services. Volunteers should be sent early. The island's battered network of roads will need to be restored quickly, and the US ought to assist in this effort.
Such actions will not in themselves end the controversy over the US invasion. But they would go a long way in disproving the oft-voiced view that the main US interest in the Caribbean is simply one of preventing communism from taking hold and that the US has little concern with strengthening the relatively weak economies and social structures of the region.