The invasion of Grenada has, so far, come up roses. The fighting was quick and decisive. Casualties and civilian damage were relatively light. The main object was achieved. The Cubans and other intruders from the communist world were expelled. The majority of the citizens seem to be happy over being ''rescued'' and seem full of kind feelings toward the American soldiers, most of whom have now left.
And there are other dividends for Washington. The leaders of the revolution in Nicaragua are apparently retreating from their more extreme Marxist ways. They may even be reaching for a reconciliation with Washington. Fidel Castro's Cuba has been remarkably quiet about the business and apparently inclined to suspend its current empire-building activities.
Mr. Castro is believed to have told the Nicaraguans and the rebels in El Salvador that they are on their own and cannot expect further help from him.
Just to cap off the good side of the invasion that worked, the combat troops have all come home. There is no residual military occupaion to breed hard feelings. The police force on duty on the island is made up largely of kindred people from neighboring islands.
This does not mean Grenada will become a paradise.
As on most of the other islands in the Caribbean, population has outrun resources. Unemployment, particularly among the younger generation, is high. Economic prosperity can come only from large infusions of new capital plus emigration plus a decline in the birthrate. The main reason for the United States not doing more operations like Grenada is that to do them is to undertake heavy and continuing responsibilities for a society which is inherently unbalanced.
Not even the vastly wealthy US can afford to take on the task of raising the living standards of all the people of Latin America - unless it could also control the birthrate, which, of course, it cannot and never could.
But the immediate and happy fact is that today, less than two months since the marines and paratroopers landed on Grenada, the last of the combat troops have come home and the islanders mostly say they are glad they came when they did. Many say they are sorry they left when they did this week. But it's always better in a case like this to leave when people are sorry to see you go. It's easy to overstay a visit.
The main lesson is that chances for success are best when the place and the population are relatively small, opposition is negligible, most people want to be rescued, and the job can be done quickly and with minimum casualties and damage.
John Foster Dulles used to have a set of rules to govern when a question came up of whether to try to rescue some country from outside interference. He favored US help when asked by a government in effective control of most of its country and backed by a majority of a population willing to fight.
If Mr. Dulles had been in charge in 1965 and had applied his rules to the problem of Vietnam, it is doubtful that the US would have found itself caught up in that involvement. If Mr. Dulles were applying his rules today, the US would not be caught up the way it is in Lebanon.
True, the US was invited in by the official government of Lebanon. But the official government of Lebanon is in effective control of only the city of Beirut and its immediate environs. Israel is in control of the southern third of the country. Syria controls most of the rest either directly or through proxies. There is no evidence that a majority of the people support the official government. There is daily and painful evidence that a majority probably does not.
As for willingness to fight, it exists in Lebanon in abundant quantity and quality. But it is largely on the side of those resisting the official government and shooting at Americans who get in the way of those wanting to shoot at the soldiers of the official government.
Grenada is the ideal example of when and how an intervention can be successful. Lebanon is an example of how much trouble a country can get into when it fails to observe Mr. Dulles's rules.