The United States is an island nation - at least that's how it looks on the maps of Pentagon naval strategists.
As a result, ''maritime superiority'' and the ability to ''project power'' into any part of the world form the centerpiece of President Reagan's planned military buildup.
The President has given the Navy a much bigger chunk of the 1983 Pentagon budget than the Army or Air Force, in return for which the Navy will increase its shipbuilding plan by more than 50 percent over a year ago.
Congress has agreed in principle to a 600-ship Navy. But lawmakers are mutinous over budget deficits. Thus, the Navy will have to steam through tough domestic political straits before it can reach the point where it could confront its most likely adversary, the Soviet Union.
Aside from bipartisan concern in Congress over the economy, there is growing debate over the military strategy that makes a much more muscular Navy the keystone of a buildup in conventional forces.
Adm. Thomas Hayward, the Chief of Naval Operations, summed up the administration view before a House subcommittee last week: ''Regardless of how or where a war with the Soviet Union might erupt, our Navy will have a global fight on its hands from the early moments of hostility.''
In a radio interview scheduled for broadcast over Voice of America this weekend, Navy Secretary John Lehman explains the rationale behind achieving naval superiority: ''Equality is a standoff, a stalemate, and in a stalemate we lose because we need to get through. We have to put the Soviet fleet on the bottom if they attempt to interdict our lifelines, and nothing less.''
There is general agreement that the Soviet Navy has shifted in recent years from a coastal defense force to one that can project considerable power around the world. In some areas - attack submarines and sea-launched cruise missiles, for example - it is clearly ahead of the United States.
The generally conservative American Enterprise Institute (AEI) says the Soviets have 563 major combat ships, compared with 345 for the US. At the same time, however, the AEI recently reported that ''the generally larger displacement of US combatants gives the US three critical advantages: superior structural damage-control potential, large fuel reserves, and below-deck ordnance stores that permit them to conduct sustained assaults on enemy forces.''
When adding allied and Warsaw Pact naval units to those of the US and the USSR in the Atlantic region, the International Institute for Strategic Studies gives the US and its allies 1,601 compared with 1,490 for its opponents.
But in comparing the numbers of ''open ocean general purpose ships age 10 years or less,'' US Defense Secretary Caspar W. Weinberger puts the totals at 150 for the United States, 220 for the Soviet Union.
In looking ahead to possible future conflicts, President Carter had begun to emphasize a naval buildup. But the Reagan team has dramatically accelerated this in a way that has every sailor from admiral to seaman smiling.
The current administration has not only increased the Navy's ship construction program significantly, but it has boosted the naval aircraft building plan by 75 percent above what it was a year ago.
America's ''deployable battle force'' will have grown from 479 ships at the end of the Carter administration, to 514 by the end of 1982, to about 610 ships by the early 1990s.
This includes 6 Trident ballistic missile submarines, 17 new attack subs, 37 destroyers, cruisers, and frigates, 2 nuclear carriers, and 3 reactivated battleships. In all, 282 ships are to be built, converted, or reactivated over the next five years.
Spending authority for the Army and Air Force in 1983 is up 15 percent and 19 percent respectively, but the Navy's jumps 27 percent over 1982. The Army will get $61 billion, the Air Force $78 billion, and the Navy $88 billion.
Prof. William Kaufmann of MIT, a defense analyst who has served many administrations, notes that of the 48 additional ships above the Carter administration's last five-year plan, 38 are associated with the two additional nuclear aircraft carrier battle groups.
Here is the key point of contention between the administration and its critics. Navy Secretary Lehman argues that supercarriers, together with their aircraft and the combat ships that accompany them, represent the best in force projection, maneuverability, and sustainability. They are, he says, ''the best way to meet the war-fighting needs of our deterrent posture for the future.''
Others call them large, expensive sitting ducks that could quickly be disabled in the early days of a war.
''The growth of satellite and aerial reconnaissance makes it very difficult for US battle fleets to hide in the open ocean,'' says Sen. David Durenberger (R) of Minnesota, who has written a 200-page analysis of how defense money could be better spent. ''Under today's conditions, what can be found can be attacked from long range. And what can be attacked can quickly be crippled or sunk.''
Senator Durenberger says a stronger, more flexible Navy could be had by making the new carriers conventionally powered (at a savings of $1 billion in construction costs alone), and directing future carrier activity to medium-sized ships and smaller carriers launching V/STOL (vertical/short takeoff and landing) aircraft.
''Some of the arguments for nuclear propulsion are either illusory or self-justifying,'' says the Minnesota Republican. ''Because we are forced to spend so much more on nuclear propulsion than on oil-fired engines, we are able to buy fewer carriers. This means that we can cover fewer ocean areas at any given time.''
The Congressional Budget Office says centering some new battle groups around reactivated battleships could give the US greater naval ''presence'' sooner and at much less expense than nuclear carriers. It is also argued that spending relatively less on nuclear submarines and more on diesel-electric subs could yield several advantages: building more for less, acquiring ''quieter'' boats that can go into shallower water, and requiring fewer highly trained personnel (one of the Navy's biggest problems).
It is generally agreed that the US needs to beef up its Navy in the face of recent Soviet expansion. But Sen. Sam Nunn (D) of Georgia, a hawkish member of the Senate Armed Services Committee, recently elicited from Navy officials (as well as those from the other services) the admission that even the administration's $1.6 trillion five-year defense program would not adequately cover all the military contingencies being planned for.