In the Sinai Desert a few days ago, 800 soldiers from the 101st Airborne Division at Fort Campbell, Ky., set up camp. As part of the multinational force and observers, they will spend the next six months helping to preserve peace under the 1979 Egyptian-Israeli Camp David treaty.
Some 7,000 miles away, 293 US airmen in Australia are manning satellite tracking stations and an airbase, part of the first line of American defense against Soviet nuclear attack.
And in the Mediterranean, an F-14 Tomcat pilot braces himself as his jet is catapulted from the USS Saratoga. The fighter pilot and his wingman are off to challenge Muammar Kadafi's claim that the Gulf of Sidra is Libya's private turf. Three years ago, US Navy pilots shot down two Libyan Su-22 Fitter jets over the gulf. The F-14 is a visible sign of US resolve to any potential adversary in Europe or the Middle East.
The deployment of US military forces around the world is a hot topic these days.
Senators, miffed at what they see as less-than-adequate defense spending by NATO allies, threaten to recall American troops from Europe. A new government in New Zealand talks about keeping US nuclear-powered and nuclear-armed ships out of their ports. Senior officers publicly grumble about Congress's role in troop deployments under the War Powers Resolution. And the Reagan administration, mindful of its militaristic image and an approaching election, announces scaled-down military maneuvers in Central America.
Meanwhile, as officials talk about the need to confront Soviet expansionism around the world and the US continues its unprecedented peacetime military buildup, questions are being raised about the goals of ''maritime superiority,'' ''forward defense,'' and ''horizontal escalation.''
Since the Vietnam war, when more than 1 million soldiers, sailors, airmen, and marines were stationed abroad, US overseas troop deployments have held at about half that number.
According to most recent Pentagon figures, 531,244 active duty military personnel are abroad (including 82,501 aboard US naval vessels). Added to this are 87,049 Defense Department civilians posted overseas. Another 396,122 spouses and children accompanying uniformed and civilian military personnel are tangible proof - cynics say hostages - that US forces would fight if attacked abroad. This means that just over 1 million Americans connected with the military services are spread around the world today.
Some 324,000 American servicemen and women are assigned to NATO, a quarter of a million of those in West Germany. The other large overseas military contingents are in Japan (45,651) and South Korea (40,791). In all, the US uniform can be seen in 118 countries. Most of these are fairly small military attache units assigned to American embassies.
Lt. Gen. Robert C. Kingston, commander in chief of the US Central Command (formerly the Rapid Deployment Force), would love to have a base of operations somewhere in the 19 countries of the Mideast, Horn of Africa, and South Asia that he oversees. But, for now, he must content himself with a home base in Florida and a ''forward headquarters element'' afloat in the Persian Gulf.
The US Navy also keeps a contingent of nearly 1,500 on the British-owned island of Diego Garcia to service the carriers and other combatants and support ships that increasingly sail the Indian Ocean.
Under the Reagan administration, the number of US forces abroad has grown by about 40,000. But the use of such forces in combat situations has been restrained. Most US troops quickly withdrew after the invasion of Grenada; only about 200 remain there. US marines in Lebanon burrowed in, then departed shortly after being devastated by a bomb-ladened truck. The battleship USS New Jersey and other US warships also disappeared over the Mediterranean horizon with the American pullout.
The use (or threat of use) of US force in these incidents and the quick scaling back were political decisions. They reflect both the increasing influence of senior uniformed officers since President Reagan took office, as well as the hesitancy of those who served in Vietnam to become involved in military actions lacking solid public support.
Still, the official US position is that the days of neatly defined wars in 11 /2 or 21/2 theaters are over; that any military confrontation between the superpowers would quickly become worldwide.
In their annual military posture statement, the Joint Chiefs of Staff emphasized that ''regional instabilities and other threats create complex and interrelated requirements for US military forces. Conflicts anywhere in the world immediately affect the United States and its allies, and have the potential for global implications.''
''The Soviets have expanded the global reach of their military forces, enhancing their ability to project influence and power, especially in the third world,'' Defense Secretary Caspar W. Weinberger told Congress in Pentagon budget hearings this spring. ''Large numbers of advisers, expanded foreign military sales, and increases in naval port visits, all point to greater Soviet military involvement throughout the world.''
At the same time, the US now has joint defense-treaty obligations with more than 40 other countries: most of Western Europe under NATO, Latin America under the Rio Pact and Panama Canal Treaty, Australia and New Zealand (ANZUS), and bilateral agreements with Japan, South Korea, the Philippines, and Thailand.
''American economic and strategic interests have obviously become global in scope,'' Prof. William Kaufmann of the Massachusetts Institute of Technology, told a conference at Tufts University's Fletcher School of Law and Diplomacy in April. ''In effect, they put the United States out on the international beat, trying to prevent trouble and impose law and order.''
US military strategy is to respond with forward-deployed forces. ''These forces demonstrate to allies the US commitment to the common defense,'' say the Joint Chiefs in their 1985 military posture statement. ''To the Soviets, they serve notice that an attack will be met immediately by US opposition.''
Rather than simply reacting to any Soviet aggression at the point of conflict , US policy now is one of horizontal escalation. This means striking back at an attacker's weak point - perhaps even his homeland - to force an end to the conflict on favorable terms. Expanding the US naval fleet to 600 ships and attaining ''maritime superiority,'' as advocated by US Navy Secretary John F. Lehman Jr., is part of this strategy.
So, too, is the prepositioning of more combat supplies near or in the likely theaters of conflict and the development of the US Central Command to move quickly into trouble spots.
Not surprisingly, this new emphasis on a strengthened conventional deterrent to war has its critics.
''In some quarters, the emphasis on 'horizontal escalation' is regarded as provocative even though the psychology of deterrence is based on the perceived ability to escalate the conflict to undesired levels,'' Jacquelyn Davis, executive vice-president of the Institute for Foreign Policy Analysis, observed in a paper delivered at the Fletcher School conference on American global strategy.
Other experts question the costs and benefits of far-flung US military deployments.
Former Pentagon analyst Earl Ravenal calculates that $129 billion in annual US military resources are focused on Europe, $47 billion on Asia, $47 billion on the Persian Gulf, and $59 billion on rapidly mobile forces poised for foreign intervention. This adds up to the total defense budget (not counting strategic nuclear forces) and includes everything from camouflaged flashlights and a private's paycheck to aircraft carriers.
In calling for a policy of ''war avoidance and self-reliance,'' Dr. Ravenal (now a professor of international relations at the Georgetown University School of Foreign Service) argues for a ''course of disengagement.'' In a study for the Cato Institute in Washington, he maintains that ''the list of feasible interventions is far shorter than the list of desirable ones, and is even shorter than the list of 'necessary' ones.''
This challenges the fundamental assumption that US security is best protected by deploying large forces away from American shores, and it reflects the kind of sentiment that Secretary Weinberger has characterized, and warned against, as ''isolationist.''
Such sentiment was part of the recent attempt by some members of Congress to demand a reduction in US forces in Europe if the other NATO partners fail to increase their defense spending at a higher rate. This was also a recognition that (as most analysts now agree) the US is more likely to face conflict in other parts of the world than it is to be drawn into a NATO-Warsaw Pact war in Europe.
''Even nonrevolutionary states are increasingly willing to disrupt the postwar order by challenging one of its key precepts, the sanctity of borders,'' Harvard University government Prof. Eliot Cohen writes in The Public Interest magazine. ''The resort to force is more common, and less likely to run into international resistance, than ever before. The diffusion of military technology . . . has enabled these third powers to fight local forces of superpowers on relatively equal terms.''
Dr. Cohen likens the US these days to the British Empire in its waning days, overcommitted around the world and forced to restructure its forces and reexamine foreign policy goals.
''Perhaps America's real military strength has grown (if one relies on arbitrary measures of sheer firepower), but what matters is its strength relative to its needs,'' he warns. ''This has declined, and declined sharply.''
Sen. Sam Nunn (D) of Georgia, one of Congress's leading defense experts, says he believes US forces are ''stretched too thin.'' Similarly, the Joint Chiefs of Staff have warned that it could cost much more than even the Reagan administration envisions to fulfill all of today's declared military goals.
When asked which weapons or forces are expendable in order to reduce defense spending, Secretary Weinberger typically turns the question around. You tell me which treaty commitments to break or allies to abandon, he says.
It is a political answer to a political question. Meanwhile, however, half a million uniformed Americans watch and wait in outposts around the world.