Why Sudan's leader is flying to the US on an emergency mission

There is an urgency about Sudanese President Jaafar Nimeiry's visit to Washington this coming weekend. He is coming despite his announcement this week that he intends to reshuffle his Cabinet and despite the sudden upsurge of fighting on Sudan's border with Chad.

So why is the visit still on?

Because (from Washington's point of view) Sudan is so strategically important and (from Khartoum's point of view) there is a desperate need to do something about the country's worsening economic plight.

In strategic terms, Sudan is the single biggest piece of real estate in Africa under a single national flag. It is the back door into Egypt. It sits astride both the Blue and White Niles and therefore has an almost absolute control of the water without which Egypt cannot live. It has common borders with Libya and Ethiopia, two countries that have close associations with the Soviet Union. And it has a coastline across the Red Sea from Saudi Arabia.

Proof of Sudan's importance in US strategic planning is seen in the country's inclusion among those where the current American ''Bright Star'' exercises in the Middle East are being staged.

As for Sudan's economic woes, its total indebtedness is more than $2 billion. It is behind $800 million on servicing its debts. Thirty-five cents of every dollar it earns should go on debt service, but its imports are costing roughly three times what it earns from exports. Half of those export earnings are earmarked to pay for oil imports. Agricultural output, the biggest export earner , is falling. And the inflation rate is roughly 50 percent.

The International Monetary Fund (IMF) has already provided several hundred million dollars in balance-of-payment assistance loans. Saudi Arabia has helped in this direction, too. There is a Sudanese request before the IMF for more loans, and General Nimeiry's Washington visit is almost certainly connected with this.

So, too, were decisions announced simultaneously with the reshuffling of his Cabinet. These included: a 12.5 percent devaluation of the Sudanese pound; abolition of the petroleum price subsidy; and the phasing out over the next 18 months of the sugar subsidy.

The IMF had indicated that the Sudanese government would have to take these austerity measures if more loans were to be favorably considered. Most outsiders agree that it took considerable political courage on General Nimeiry's part to go ahead with them.

The proposed wholesale reshuffling of the Cabinet is apparently intended as a dramatic move to bring home to Sudanese public opinion the country's economic straits and the inevitability of drastic steps to deal with them.

In Washington, General Nimeiry can be expected to point to the bold moves he has been prepared to take at home and to ask both the IMF and the Reagan administration to reciprocate as generously as possible with economic aid.

Most outsiders who have dealings with the Sudanese come to admire them for their integrity and independence. So there is an almost unmerited cruelty in so many chickens coming home to roost at the same time to produce such a grim economic situation. These include:

* The stiff increases in oil prices over the past decade.

* Misplaced enthusiasm in the mid-1970s about turning Sudan into a breadbasket with the help of loans from oil-rich Gulf states. Insufficient heed was paid to the country's lack of infrastructure (particularly roads), and the terms of loans made available were basically unsuitable.

* Cotton farmers discovering in the early 1970s that they could make more and quicker money by deserting the government-run cotton-producing program and switching to grain. Cotton is back as the best earner on the export market, but farmers are reluctant to come back under control of the government bureaucracy.

* A white fly infestation that makes cotton sticky for ginning and that consequently reduces the price that Sudan cotton can command on the world market.

* Unusual rains that caused devastating flooding in the Gezira cotton-growing area and resulted in this year's crop being the worst ever.

* The continued lack of infrastructure and communications, with Port Sudan - the country's only major maritime outlet to the world - perched on its eastern rim far from the population centers on the two Niles and even farther from its western provinces, such as Darfur.

* Departure of the top university graduates for better-paying jobs in Saudi Arabia and other Gulf states.

* Arrival of tens of thousands of refugees from strife-torn countries such as Chad, Uganda, and Ethiopia/Eritrea. Some estimate there are as many as half a million.