The top military leaders who took over Nigeria peacefully New Year's Eve are not sleeping all that peacefully these days. There is now substantial evidence to confirm earlier speculation that the Dec. 31 coup was a preemptive move to head off more radical junior and middle-rank officers from seizing power from the civilian government.
The unsettling question for the new regime is whether leaders of this lower military faction will regroup and attempt a countercoup if they think the military rule of Maj. Gen. Muhammad Buhari is not coming up with answers to the nation's tremendous difficulties.
So far the military government has been welcomed with almost evangelical fervency by a public that feels it has been delivered from a hopeless economic situation by the Army's intervention.
A food expert suggests that many of Nigeria's problems were artificially induced, at least in the crowded region around Lagos.
''The very people who took time to vote in the last election had no food to eat, had no water, and very often no electricity,'' he said.
''Some people had to wait at the harbor for ships to bring in food which could be easily grown in this country. What was worst was that the food was actually imported when other food was being hoarded and released bit by bit to sustain the high prices.''
Performance in office, not accession to power, has rapidly become the criterion of public acceptance of the Buhari rule.
On that score, Nigerians see no reason to question the intentions of a government that is practicing a low-key lifestyle, preaching austerity, and winning friends by opening up warehouses of hoarded goods.
But a coterie of lower-rank officers, miffed at being thwarted in their plans to overthrow the former civilian government, are apparently not yet reconciled to the new military leadership under Buhari.
Although a countercoup is not considered imminent, this newspaper has learned that these lower-echelon officers pose a challenge because they do not hide their disapproval of the new leadership.
What they are saying is that the Buhari regime is not the government they want.
According to authoritative sources, the charges being leveled against General Buhari's one-month-old regime include:
* It is not moving fast enough to repair the damage caused by a profligate civilian government and reflects no real change in policy direction. To some extent, the new administration has tried to maintain a sense of continuity where possible. It has kept the judiciary intact and reappointed the powerful permanent secretaries in the civil service.
* It includes within the Supreme Military Council, the top policymaking body, some senior officers who are suspected by these military critics of being just as guilty of having ''sticky fingers'' as the repudiated civilian officeholders before them. So, these disaffected officers want to know what's the difference between the old and new leadership lineup.
The possibility of a countercoup leaves many foreign diplomats here uneasy.
They note with satisfaction the credentials of the new government, split between military and civilian appointees. They are concerned that a countercoup might usher in a more radical - and less responsible and less experienced - team of administrators.
According to reliable information, the new military government has attempted to strengthen its position by promoting some officers and flushing out those who apparently did not go along with the coup or who were viewed as opposing the Buhari coup.
Analysts familiar with the situation suggest that the likelihood of impatient soldiers waiting in the wings is a powerful incentive to General Buhari to make radical changes in government policy.
The next two to three months are considered critical. Three things are seen as essential for General Buhari's government to survive:
1. Gaining new international commercial credits, particularly from European banks which have a higher financial vulnerability in Nigeria than United States banks.
Such a deal, however, is contingent on:
2. Secure a loan from the International Monetary Fund.
Nigeria has been negotiating on and off for a $2 billion loan to ease its balance-of-payments difficulties. The loan would enable the country to bring in valuable foreign exchange to buy needed materials to boost the country's sagging economy.
A Western diplomat reviewing Nigeria's financial predicament says: ''It's going to be rough. The government keeps on saying it must cut its coat according to its cloth, but when it starts to inspect the cloth, it finds it has a very ragged coat indeed.''
3. Announce a government budget that would signal how the national pie will be sliced and what the government priorities are.
High on the priority list is almost certain to be an overriding commitment to agriculture. Until oil profits lured people away from the land, Nigeria was the continent's largest exporter of food. It has now become Africa's largest food importer, forced to spend precious foreign exchange.
For this reason the harvesting of crops in July could be a turning point in assessing the Buhari government's chances of survival. Equally important, these analysts say, is the twin development of oil and natural gas. Nigeria is blessed with enormous reserves of natural gas, but development is a highly costly business.
Diplomatic observers say the magnitude of the country's problems is not beyond the ability of the Buhari government.
To hang on, however, it must soon produce tangible gains.