LAGOS, NIGERIA — A FOILED coup in oil-rich Nigeria points out the instability of the military regime under Gen. Sani Abacha, who seized power 18 months ago from the country's interim president ''for a brief tenure.''
The government announced Friday that it had foiled a coup attempt planned for March 1 by military officers, its first public admission of the plot.
Maj. Gen. Abdulsalam Abubakar, chief of defense, in a press conference gave no details of how the coup was to have been carried out or how it was foiled. He also refused to identify those being held.
General Abubakar blamed the latest plot on ''a group of overambitious and misguided officers and civilians.''
The plot signals discontent with General Abacha's hard-line government, which took power from interim President Ernest Shonekan in November 1993, after the military reneged on promises to return Nigeria to civilian rule.
Abacha has jailed scores of opponents, and the resulting political unrest has led to economic problems and more instability.
The Nigerian regime's preoccupation with internal threats is a distraction from the tasks facing the government, which still has no schedule for handing over power. For the last month it has not even had a Cabinet.
A constitutional conference recently recommended a return to civilian rule by January 1996, but hard-liners are pushing for a delay.
The recent military arrests underline the international isolation that besets Abacha's regime.
Nigeria is West Africa's natural leader by virtue of its greater size, but has alienated its allies by clinging to corrupt bureaucratic control of the economy and military dictatorship.
While the president of neighboring Ghana, Jerry Rawlings, met with President Clinton at the White House last week, Nigeria's rulers have been barred from direct official contacts with the United States and the European Union as a protest against the continuation of military government. Mr. Rawlings has accomodated the West's demands for liberal economic reforms and a democratically elected government. (Special report on Africa, page 9.)
Last week, after tough lobbying at the UN Human Rights Commission in Geneva, Nigeria's attorney general succeeded in defeating a vote of censure on Nigeria's human rights record.
On March 7, Lynda Chalker, Britain's overseas aid minister, backed a call by Nigeria's constitutional conference last year for the military to leave office by the start of 1996, and said the EU deplored the repressive decrees promulgated in 1994. ''These [decrees] prescribed press freedoms, strengthened powers to detain without trial, and withdrew habeas corpus.... Nigeria is failing to live up to its human rights obligations,'' she said.
Aminu Saleh, head of Nigeria's civil service, denied that the government is slow to hand over power to civilians, but wants ''perfection in its administration of the country.''
''Whatever we want to do on the political program will depend on the outcome of the constitutional conference,'' he said in a recent interview. ''We are not saying that it will do everything, but at least the government structure should be based on what is in the draft.''
The draft for a new constitution was virtually ready in early December, but the delegates voted for a Jan. 1, 1996 handover to civil rule. Since then, the conference has spent most of its time in recess. Conference chairman Justice Adolphus Karibi-Whyte said recently that the delay now made the 1996 handover date unrealistic.
In private, the power-brokers at the conference admit that their draft amendments make very little change to the Constitution, while the delays and ultimate annulment of the previous regime's eight-year transition program have undermined the credibility of the Army's promises about handing over power. Political parties remain banned.
Furthermore, Moshood Abiola, who won the annulled presidential election in June 1993, is entering his ninth month in detention, facing charges of treason for declaring himself president.
Several of Mr. Abiola's supporters, including trade unionists who led an oil strike to back him last year, are also in jail without trial.
A leading commentator in Nigeria for the Constitutional Rights Project (CRP), has described 1994 as ''Nigeria's worst year regarding human rights.''
In a recent report, the CRP records at least 120 killings by police and other security agencies, including those demonstrating against continued military rule.
''Draconian military decrees circumscribing fundamental rights and giving immunity and impunity to the military junta have been promulgated,'' says Clement Nwankwo of the CRP.
''Accountability and responsibility of the junta's officials are nonexistent, and the country is at its worst, politically and economically,'' he says.
''Things seem to be drifting,'' says Beko Ransome-Kuti of the Campaign for Democracy, a nonparty political pressure group. ''But we can't go on like this. Something has to give.''