The multitude of press briefings and declarations in official Washington Tuesday carried a multitude of explanations for United States intervention in Grenada. But it was increasingly apparent that underlying and overlaying all other expressed concerns, such as the safety of US citizens, was the administration's concern over the spread of Soviet and Cuban influence in the Caribbean and Central America, and more specifically its desire to stop the emergence of a ''second Cuba'' in Grenada, a development it has feared since Maurice Bishop took power in 1979.
The administration's action and the basic premise underlying it are topics of fierce debate. Much of this debate focuses on the answers to four questions:
1. How important is Grenada to the US and to regional security?
2. Was Grenada under Maurice Bishop rapidly becoming a second Cuba and a threat to the US?
3. Were the Cubans and Soviets behind last week's coup by Grenadan Deputy Prime Minister Bernard Coard?
4. Would they have taken advantage of the coup even if they were not initially behind it, turning Grenada into a Soviet satellite?
Those justifying the invasion stress, among other things, Grenada's geopolitical significance. They emphasize the island's proximity to the Panama Canal and the oil fields of Venezuela.
However, close analysis of Washington's statements indicates that the main fear for both Washington and its Caribbean partners-in-invasion was probably the domino theory. It was felt that any communist takeover of Grenada might begin to tilt the balance in the region and eventually throw the entire eastern Caribbean into Cuban arms.
From the point of view of the Reagan administration, a pro-Soviet Coard-controlled Grenada would have come on top of what it sees as a basically communist regime in Nicaragua, an extreme radical government in Suriname, and serious Soviet-inspired threats to the pro-US governments of El Salvador and Guatemala.
But unlike some of the other countries on this list, the radical regime in Grenada could probably be dealt with swiftly and with relatively little military and political cost.
Some see the invasion as a message to Nicaragua. Secretary of State George Shultz stated Tuesday that there was no such message. This is possibly the case.
Although administration officials are not averse to striking fear and trembling into Sandinista hearts on the cheap, close observers of the Caribbean scene say that realists in the administration - like Secretary Shultz himself - must know that because of the size of the country, the determination of those in power, and the difference in degree of popular support for the Coard regime on the one hand and the Sandinistas on the other, an invasion of Nicaragua on the Central American mainland would be far more costly in both real and political terms than the present intervention in the spice island of Grenada.
Neither Bishop nor his regime was easy to label.
Bishop claimed Cuba's Fidel Castro as his lifelong idol and model, and used Cuban advisers throughout his government. While no tyrant, he was autocratic in style, censoring the press and discouraging strong public criticism of his regime.
Most threatening to the US, Cuban workers helped build an airport that might have become a Cuban air base.
Bishop's government may have belonged to what could be a new hybrid, a Marxist-oriented government that does not follow classic communist lines. The main question for the US is: Are such governments necessarily pro-Soviet or can they be coaxed into a more neutral posture, happily playing the two superpowers against each other.
Some observers have long felt Castro's real ambition is to free himself from his dependence on the Soviet Union by heading a radicalized Latin America that would not follow the same orthodox communist economic model he did and that would not be tied to either great power. Under to this theory, Bishop's regime would have been the kind of government Castro would be likely to encourage.
There are still few indications that Cuba was behind the Coard coup. On Thursday, Mr. Shultz stated that the US had ''no direct information'' on Cuban involvement but that the invading Caribbean countries felt that this was the case.
In her joint press conference with President Reagan, Dominica's Prime Minister Eugenia Charles spoke of conspirators seen entering and exiting the Soviet Embassy in the weeks before the coup. Some Caribbean observers point out that most high-level Grenadian officials frequently visited the Soviet Embassy long before any talk of a coup. Press reports on Wednesday stressed that OECS leaders thought talk of Soviet-Cuban backing of Coard would be a useful tool in obtaining US intervention.
Cuba probably did not oust Bishop. But had Coard and his group remained in power and shown themselves eager to join the East bloc, it is unlikely they would have been refused. In the same statement in which Cuba condemned Bishop's murder, the Castro government said it would not break off economic cooperation. Unlike some of the other players on the Caribbean scene, Castro was leaving his options open.