IN foreign affairs the priority item on Ronald Reagan's second-term agenda is obviously the rolling back of communism and Soviet influence in Central America. He has already made noticeable progress in bolstering the moderate Duarte regime in El Salvador. Obviously he still hopes to overthrow the existing regime in Nicaragua, or at the very least see it reform itself away from its current Marxist inclinations.
But he shows a surprising reluctance to use more than rhetoric against the most flagrant act of international aggression committed by the Soviet Union since World War II.
Last Dec. 27, the fifth anniversary of the Soviet invasion of Afghanistan, Mr. Reagan called the event ``a day of infamy.'' But Congress has taken the lead in wanting to do something tangible to help the Afghan people in their tenacious attempt to survive under the weight of an invading army of more than 100,000 Soviet troops.
Officially, there is no United States aid to Afghan guerrillas. There are no official figures on what is being done. But it can be stated on information from officials who were speaking unofficially and ``off the record'' that the administration had budgeted somewhere around $150 million for such aid during the current fiscal year.
A bipartisan move in Congress raised the amount to about $250 million. And if Congress had its way, the figure would go higher. Both Senate and House have passed unanimous resolutions calling for effective support for the Afghan patriots battling the forces of the invader. Liberals stand shoulder to shoulder with conservatives in this cause.
The trouble is that helping the Afghan guerrillas is one of the most difficult tasks of its kind in today's world.
The US is not the only country trying to help. Military aid goes to the guerrillas from Egypt, Saudi Arabia, and China. There is a single mountain track from China to the Afghans which the Soviets have not yet closed. Convoys can get through by that route in the summer. Not much can cross the mountain passes over the Himalayas in winter. If Iran were still on friendly terms with the US, heavy support could go that way. But Ayatollah Khomeini is not on speaking terms with Washington. The Iranians have given help to the Afghans on their own, but their resources are so heavily committed to their own war with Iraq that they have little to spare for the Afghans.
The only practical way to get supplies in quantity into Afghanistan has to be through Pakistan. And Pakistan is uneasy about any substantial quantity. Pakistan would help if it dared. It gives a place of refuge to a huge number of Afghan refugees. Much American aid has to go just to feed and shelter those refugees who would otherwise be an intolerable burden on the Pakistan economy.
The real trouble is that if large quantities of US aid were to cross Pakistan on its way to the Afghan guerrillas, Moscow could treat it as an excuse to invade Pakistan itself. As a practical matter the flow of aid through Pakistan is kept below the level at which it is calculated that the Soviets might decide to strike.
Few doubt that if a favorable opportunity arose for the Soviets to march to the Indian Ocean over Pakistan, they could not resist the temptation, even though it would rouse the whole Muslim community to resentment.
The surest way to get outside weapons to Afghanistan would probably be to fly them in from China. But that would be to risk Soviet air attack on the planes carrying the aid. It would probably have to be done at night, if at all. And then there would be the problem of dropping the supplies into Afghan hands. The Soviets control all the airfields and the main highways.
The net result of the many limiting factors is that enough aid can get through to the Afghan guerrillas to keep up their hopes and their guerrilla warfare, but probably not enough ever to give them the capability of a decisive military victory.
All of which explains why it is easier to condemn what the Soviets are doing in Afghanistan than it is to give effective support to the guerrillas.