The United States now could swiftly fly a small but heavily armed land force to defend Persian Gulf countries, but probably could not successfully oppose an overland Soviet invasion of Iran, say independent US defense analysts.
Because the US lacks bases in the area and is low on sealift and airlift capacity, outside analysts -- including at least one former US service secretary -- have strongly advised the Carter administration against involvement in any land war in South Asia, from Iran eastward to the China Sea, for the next decade.
Stung by the contentions of members of Congress, including Sens. Henry Jackson (D) of Washington and Harry Byrd (D) of Virginia, that the US is powerless to check further Soviet advances, Defense Secretary Harold Brown and Gen. David Jones, chairman of the Joint Chiefs of Staff, both have said the US can move militarily in the Gulf area. But both admitted in testimony before congressional committees there could be no certainty of victory in a South Asian or Gulf conflict.
Exactly how quickly the US could move now, a year from now, and after President Carter's proposed five-year defense buildup (which many congressmen say falls short of what is needed), was spelled out by senior Pentagon Officials under ground rules forbidding use of their names:
* If hostilities erupted now in the Gulf, and one or more local governments asked for US help, the two US aircraft carrier divisions now in the Arabian Sea could be bolstered within 48 hours by two squadrons (about 36 planes) of tactical aircraft and an AWACS flying radar and battlefield control plane from the United States or Europe.
One battalion of either the US Army's 82nd Airborne or 101st Air-Mobile Division could arrive within 48 hours from the US, provided the host country did not oppose their landing. Another unit, the Army's 509th Airborne Battalion, now stationed in northern Italy, could also get there, bringing more than 3,000 men with heavy equipment.
The US Marines could respond with one air squadron within 48 hours and could move a marine amphibious unit (MAU) with 2,200 men and helicopters through the Suez Canal from the Mediterranean within nine days. If more marines were needed , another MAU could arrive by sea from Akinawa or Subic Bay, Philippines, in 10 to 14 days.
Equipment for a full marine airborne brigade, including armor and artillery, could be sealifted in two weeks. A further 7,900 men of one heavy Army mechanized brigade, with 55 M-60 and 126 M-113 armored personnel carriers, would require 14 days from the US East Coast.
A greater buildup, if needed for a land conflict with the Soviets or surrogates in Iran, Iraq, or Pakistan, could be carried out by stripping US forces in Europe of much of their air-supply capacity, including C-130, C-141, and C-5A transport planes. Supplies stockpiled in Europe could be picked up on the way; but after five days in the Gulf area there would be need for permanent, defendable air-and sea-supply lines.
By the end of 1980, the Pentagon plans crash procurement of ships, enabling pre-positioning of supplies for one marine brigade equivalent (about 8,000 marines) in the Indian Ocean. The marines could be flown from the US within 48 hours and could be added to forces available now.
The Pentagon wants to negotiate purchase of three big roll-on, roll-off (Ro-Ro) ships and seven or eight fast container ships. The Ro-Ro ships would cost $60 million or $70 million.
By 1984 to 1987, more than 100 of the projected new CX cargo planes, big enough to carry heavy armor -- including the new Chrysler XM-1 main battle tank -- plus new C-141 planes and KC-10 tanker aircraft for airborne refueling, would be ready.
The entire US rapid deployment force -- a total of 110,000 to 150,000 men, with all needed equipment, plus air and sea support -- could then move to the Indian Ocean, Persian Gulf, or Arabian peninsula in 30 to 45 days, depending on the logistics en route and the scenario.
The US, Pentagon officials soberly warn, is not ruling out the use of "theater" (medium-range) nuclear weapons in theaters other than Europe, where they are already deployed. Such theaters include the Gulf/Indian Ocean region.