A sweeping land reform carried out here four years ago has run into serious economic difficulties despite its enormous popularity with the peasants and success in rallying their support for the Ethiopian revolution.

Some of the problems stem directly from what a recent government brochure calls "The agonies of war" that have afflicted Ethiopia since shortly after the military deposed the late emperor Haile Selassie in 1974 and set this once sleepy feudal empire on a radical Marxist course.

"Four years of brush fires, battles and a naked aggression (by Somalia) have left their mark on all sectors of the economy," the brochure remarks "Other countries have successfully won revolutionary wars and built up their economies, but revolutionary Ethiopia inherited a fragile economic infrastructure which has been weakened by four years of constant war."

But the key issue for the military government has become how to get the peasantry, now organized into some 25,000 semiautonomous associations, to produce more, and above all sell more, to the food-short towns and cities where 3 million of Ethiopia's 30 million people live.,

Some outside Western analysts wonder whether the government will have to resort to a "green terror" to extract by force more food grains and cash crops from the peasant associations. It has already carried out a very effective "red terror" to eliminate its leftist and rightist opponents.

For the moment, the government is counting mainly on "agitation" and "political education" to persuade the peasants to cooperate voluntarily with its recently launched "national revolutionary development campaign."

In the past two years, the economic situation here has deteriorated sharply. The government has exhausted its once relatively large foreign exchange holdings, mainly buyiung Soviet arms, and it is now having trouble paying for essential imports.

Last year, food grain production fell by 600,000 tons and Ethiopia had to import 240,000 tons. Estimates of this year's import needs range as high as 300,000 tons.

The main export crop, coffee, which provides well over 60 percent of Ethiopia's foreign exchange earnings, has fluctuated greatly over the past three years, from a low of 43,000 tons during the 1976-77 harvest to 74,000 tons last year. Higher coffee prices in 1976 assured earnings almost as high as last year's $289 million.

The government's development campaign has set three aims: boosting of food crops to the point of self-sufficiency; vastly expanding coffee and other export crops, and laying the foundations for a new socialist economy.

To do this, the government has decided to put the country virtually on an economic "war footing." It has set up a Central Planning Supreme Council directly under the Military Council chairman, Lt. Col. Mengistu Haile Mariam, and set up promotion offices at all administrative levels.

Ethiopians say the Supreme Council is already more powerful than the existing Council of Ministers and issues order to Cabinet members.

The plan calls for the peasants to increase production by up to 400,000 tons and state farms by 170,000 tons. Coffee exports are supposed to jump to 100,000 tons and industrial output is to expand by 42 pecent-all in one year.

Most Western economists here as well as Ethiopians Regard these goals as unrealistic, except perhaps for the state farm sector, where 13 new units have already begun opening up an additional 198,000 acres of land.

They estimate that grain production this year will be about the same as last and that coffee exports may not reach much beyond 60,000 tons. As for industrial growth, they say much depends on the war in northern Eritrea Province where 25 percent of the country's industries are located.

Western predictions about most events in Ethiopia have been wide of the mark and these may be, too. An unknown factor is the reaction to the development campaign of the war-weary peasants. They have gained land, political power, arms and wealth as a result of the land reform but are also close to being beyond government control.

Indeed, the country's Marxist ideologists are up in arms about the mushrooming of a whole new class of "kulaks," or rich farmers, who they say have taken over the leadership of many peasant associations, are opposing collective and cooperative farming schemes and are hoarding grain and coffee to force up prices.

Kadir Mohammed, secretary general of the year-old All Ethiopian Peasants' Association, regards these farmers as "the biggest obstacle to our revolution today.

"It is a class that has grown up since the land reform made the peasants owners of the land. It is still growing and a great danger," he said in an interview.

Western economists here agree there are many new rich peasants, particularly in the coffee-growing areas where some of them have taken to drinking imported Scotch rather than the local beer.

But they see other roots for the production problems. They say the land reform destroyed the hold of the landlords over the peasants and thus the main mechanism for marketing their crops and distributing consumer goods in the countryside.

"The peasant simply has no incentive to produce more," remarked one Western aid official. "If he does, what can he do with the money? There is nothing to buy. He'd rather keep the grain and eat it himself."

"It's a matter of educating and convincing them that it is in their own interest to sell their grain or coffee," said an optimistic campaign official. "We rely on education, not force. We believe that if things are explained to them, they will cooperate."