ADDIS ABABA, ETHIOPIA, SEPT. 13 -- It is happening again.

The rains have failed in the north and central highlands. Fields of grain are wilted, dying or dead. About 5 million people are estimated to be at risk. Ethiopia, the world's poorest country, is sliding inexorably toward another food emergency.

The government here asked western donors last week for about 1 million tons of food, only slightly less aid than the West delivered in 1985 in the world's largest food relief operation in history.

Western donors agree that a sudden and severe drought in June and July has made Ethiopia vulnerable to another famine. Rainfall in some areas was as low or lower than in 1984 and 1985. Donors said Ethiopia's food request, if anything, understates the seriousness of the coming food shortage.

The U.S. Embassy late last week sent an emergency request to Washington asking that 115,000 tons of food be dispatched here immediately. The European Community and the U.N. World Food Program are considering requests for immediate shipment of another 85,000 tons of food. It takes four or five months for promised food to be delivered to Ethiopia's rural highlands.

The Ethiopian government and major donors warn that unless about 200,000 tons of food aid arrives here by the first of the year, famine conditions, with mass movements of destitute and starving people, will begin in the northern regions of Eritrea and Tigray.

A U.S. government survey last month reported a total crop failure in Eritrea and a 75 percent crop loss in Tigray.

As particulars on the drought were released here, an elaborate, week-long national celebration in this capital evoked an eerie sense of deja vu.

More than 7,000 goose-stepping Ethiopian soldiers paraded today through the city's Revolution Square. They were followed by rows of Soviet-made tanks, rocket launchers, field cannons and 20-foot-long missiles. Tens of thousands of uniformed children and young adults also marched, waving red flags, plastic and paper flowers. Men chanted, "Forward." Women ululated and fluttered their shoulders in traditional Ethiopian fashion.

The entire city has been dressed up in red, green and yellow bunting. Fresh red paint has brightened the city's ubiquitous billboards of Marx, Engels and Lenin. At night, government buildings blink and blaze with Las Vegas-like neon displays glorifying the country's 13-year-old Marxist government.

The celebration marks the death of the military government headed by Col. Mengistu Haile Mariam and the birth of the People's Democratic Republic of Ethiopia headed by President Mengistu Haile Mariam.

Exactly three years ago, during celebrations of the 10th anniversary of the overthrow of Emperor Haile Selassie and the creation of the Workers' Party of Ethiopia, word began to reach the outside world of a catastrophic famine in this country.

Then, the daily death rate was already about 16,000 a day in famine camps in the countryside. The figure comes from Dawit Wolde Giorgis, who headed Ethiopia's famine relief commission at the time and has since defected to the United States. According to Dawit, Mengistu sought to cover up the famine, ordering him to "keep the soldiers and the Addis population satisfied until the celebration was over."

In a speech in July, Dawit told the Royal Institute of International Affairs in London that "when Mengistu heard reports of the ragged mobs of skeletons approaching Addis, he finally acted. The police were instructed to make a human fence to keep the starving from entering the city and spoiling the show."

This year, despite the dovetailing of celebrations and warnings of an impending food emergency, there appears to be no attempt by the Ethiopian government at a cover-up.

The head of the government's Relief and Rehabilitation Commission, Berhanu Jembere, sent a letter last week to the senior U.N. official here asking for 950,000 tons of food for 1988.

The need is four or five months off. Thus far, according to relief officials, people in drought areas still have access to food. There are no famine camps and no reports of large numbers of deaths.

Berhanu told donors last month that the government does not intend to allow the food shortage to deteriorate to the point where television cameras will find starving people. The plan, he said, is to supply food to people in their home regions and avoid mass migrations to famine camps.

The U.S. government, too, wants to avoid the accusations that tainted its sluggish response to the 1984-85 famine. Then, according to a number of authoritative reports after the famine, distaste for Ethiopia's politics delayed relief operations by the Reagan administration. In the end, after widespread outcry by the American public, the United States was by far the largest single food donor.

"There will be a more sophisticated response this time," said James Cheek, charge d'affairs at the U.S Embassy here. "There won't be a GAO {General Accounting Office} report on this one."

On a more fundamental level, however, there are compelling similarities between the 1984 famine and the emergency unfolding here.

As it was three years ago, Mengistu's one-man government remains one of the world's most rigidly orthodox Marxist regimes.

That orthodoxy, according to agriculture specialists from both the West and the Soviet Union, limits this nation's ability to feed itself and makes it unnecessarily vulnerable to famine.

Ethiopia has resisted the free-market farm reforms that have swept across Africa in the past three years. Avowedly socialist countries such as Tanzania have instituted reforms that pay higher prices to farmers. The results of such reforms in Tanzania, and across Africa, have been encouraging. Ethiopia has not budged.

Indeed, this government has shown little or no interest in farm reforms in the Soviet Union, Mengistu's ideological mentor and military patron.

In a six-hour speech last week, Mengistu made no reference to the reform movement in the Soviet Union, nor did he mention the concept of monetary incentives for farmers.

He did not mention that small private farmers are by far the most important component of Ethiopia's economy, accounting for 40 percent of the gross national product, 85 percent of exports and 80 percent of employment, according to World Bank figures. Nor did he mention that state-owned farms absorbed about 40 percent of all government expenditure on agriculture between 1980-85 while contributing about 4 to 5 percent of total food production.

Instead, Mengistu insisted that "our effort of socialist construction can bear fruit only if the private sector in agriculture is replaced by a socialist property sector."

The speech disappointed representatives of western donor governments that again are being asked to supply relief food.

It also appeared to ignore the advice of a 1985 consulting report by Soviet advisers. That report concluded that Ethiopia should turn its attention away from expanding state farms and producer cooperatives and, instead, concentrate its limited resources on increasing the productivity of small farmers.

"The West and the Soviets are only asking this government to imitate modern, progressive socialism as practiced in the rest of the world," said one senior western diplomat here.

With Ethiopia facing a severe drought and food shortage just three years after its great famine, it is clear to many farm-policy experts that this country's chronic food problems are far too complex and intractable to be solved simply with higher prices for farmers.

"This time around, I don't think reforms would have made any difference," said Nicholas Winer of Oxfam, a British relief agency.

Ethiopia's farm economy is extraordinarily susceptible to drought. This year's crop was expected to be above average until the rain stopped abruptly in June. Ethiopian historian Moefin Woldo Mariam said the country can expect local droughts every year, regional droughts every three or four years and widespread drought every eight to 10 years.

Even by the standards of Africa, the world's poorest continent, farm practices here are extraordinarily backward. Only 2 percent of crop land is irrigated; only 5 percent of farmers use fertilizer; only 2 percent use improved seeds.

For a host of reasons, farm production has stagnated in the past decade. Ethiopia's production of people, however, is booming.

The most recent estimates are that the country has about 45 million people and an annual growth rate of 2.9 percent.

"Every year in this country, there are 1.2 million more people to feed," said Ingo Loerbroks, representative here for the U.N. Food and Agriculture Organization. "The country has to hurry up its food production to stand still."

Ethiopian peasants, despite exhortations from the government to work harder, have not hurried up. According to World Bank and U.N data, per capita availability of grain in the past 10 years has dropped 22 percent.

The country's built-in or structural food shortage is growing every year. A report by the U.S. government estimates that even if the rains had not failed this year, Ethiopia's food deficit would have been about 500,000 tons. By 1990, assuming that food production remains stagnant, the report says the normal deficit could reach 2 million tons. That is nearly twice the amount of food delivered to Ethiopia in 1985.

If all this weren't enough, Ethiopia also is afflicted with three seemingly endless wars that are forcing it to maintain the largest standing army (about 300,000 soldiers) in Africa.

To the southeast, there is a simmering border conflict with Somalia. In the northwest, Tigrayan rebels have bedeviled government troops for the past 12 years with hit-and-run attacks. Farther north is a far larger, bloodier, more conventional war with Eritrean rebels. That war, the longest continuously running conflict in the world, is 27 years old and shows no signs of resolution.

Despite Mengistu's apparent reluctance in his speech last week to mix any mention of incentives with his rhetoric about "sweeping revolutionary transformation," there are some signs that his government may implement farm reform.

The EC and the World Bank are holding out nearly $300 million in grants and loans as a reward for farm reform. The Swedish government, too, has about $100 million in farm development money earmarked for Ethiopia if reforms are implemented.

"If history is any guide, considering what has happened in the rest of Africa and in the Soviet Union, this country will do something at some stage," speculated Winer of Oxfam. "We don't know when."

In the meantime, major donors said they have no choice but to try to beat the drums back home for more food and money. They emphasized that the food must be pledged immediately to arrive here in time to prevent mass migrations to famine camps, which three years ago were breeding grounds for epidemics. About 1 million Ethiopians are estimated to have died in the 1984-85 famine.