A common theme through much US foreign policy today is the limited effectiveness of military power. Hallmarks of the Reagan administration have been the rearming of America and a refusal to concede to the Soviet Union in any forum or region. In his press conference this week, the President stressed that the ''world maybe is a little safer'' because of his policies. And he boasted that the Soviets ''haven't taken another inch of territory since we've been here.''
But there are other indications that a more muscular United States also has its problems:
* The strategic buildup has not brought arms control. Indeed, former national-security adviser Zbigniew Brzezinski said this week that a comprehensive nuclear arms agreement may no longer be possible, given recent technological advances - especially accuracy and mobility - in offensive strategic systems.
''A very strong argument can be made that we've come to the end of the road in traditional arms control,'' Mr. Brzezinski told reporters over breakfast. The former adviser to Jimmy Carter agrees with the Reagan administration that strategic defense possibilites (derided by critics as ''Star Wars'') should be fully explored. And he believes that less comprehensive nuclear arms reductions are still possible.
* US options in Central America - for all the concern over military exercises and construction - are narrowly constrained by other considerations. Even senior US military officers in Latin America say it is not overwhelming military force but ''military capabilities'' - a fuzzier concept involving political and economic considerations - that will effect change there.
* NATO's deployment of new intermediate-range nuclear weapons has not brought the desired response from the Soviet Union or resulted in a Western alliance as strong as the US would like. There is concern here that Dutch hesitancy to accept new US-made cruise missiles could spread to other Western alliance countries also slated to receive the new nuclear-tipped weapons.
* US military options in the Gulf are particularly limited. This is true whether or not, as the President said, the US would employ American force there without a clear invitation from Gulf countries or - as Brzezinski argues would be mandatory - European allies join in. This can be seen in how the US Central Command (what used to be called the Rapid Deployment Force) has evolved since its creation in 1980. The administration's maritime strategy - backed by a 600 -ship Navy centered on new, large aircraft carriers - is also of limited usefulness.
The Rapid Deployment Force was formed in 1980 by the Carter administration in response to the Iranian revolution and the Soviet invasion of Afghanistan. No new forces were added to the US armed services. But the bureaucratic shift was designed to organize those forces so they could move more quickly to the Gulf region, particularly if the Soviet Union were to attack Iran. At the same time, the US began seeking bases in the region to position aircraft and ground troops.
Since then, the US Central Command has made some progress, both in increasing the US presence in the region and in prepositioning some military assets closer to the likely area of conflict. But these still are far short of what the Pentagon would like to have, and prospects for more seem slim.
The US has acquired access rights to some airfields and other military facilities in Oman, Kenya, Somalia, and Egypt. But countries in the region - despite increasing amounts of military aid and visits by high-level American military officers - are hesitant to grant US requests for more permanent basing. And the House Armed Services Committee was recently reported to have made significant cuts in administration requests for more military construction funds earmarked for those areas.
The Central Command commander in chief, Lt. Gen. Robert C. Kingston, would like to have his headquarters ashore near the Gulf. But so far he has had to settle for his command headquarters remaining in Florida and a ''forward headquarters element'' aboard a US Navy ship in the Gulf. The only relatively permanent US military site in the region is on the British-owned island of Diego Garcia - some 2,500 miles away from the sensitive Strait of Hormuz. General Kingston reported to Congress recently that the prepositioning of additional fuel, water, ammunition, and other supplies nearer the Gulf, along with the acquisition of more transport aircraft and ships, will help if he needs to deploy any of the 300,000 troops available to him.
The US also keeps an aircraft carrier task force just outside the Gulf. But because of the distance to potential military targets closer to the Iran-Iraq conflict, it would be very difficult - without land-based airfields - for carrier jets to attack those targets or to provide sustained protection to ships in the Gulf.