A SHAKE-UP in Rwanda's government reflects the diminishing clout of moderates, further fraying the fragile coalition between Hutu and Tutsi leaders. And it makes the continuing refusal of Hutu refugees to return home from neighboring Zaire difficult to overcome. Rwanda's majority-Tutsi parliament voted Aug. 28 to sack Prime Minister Faustin Twagiramungu, a Hutu. They also agreed to overhaul the government and remove an unspecified number of Cabinet ministers. Diplomats say Mr. Twagiramungu had received threats. In his letter of resignation he said he was angry at reports of killings by the Tutsi-led Rwandan Patriotic Army. Rwandan government officials, such as Maj. Wilson Rutayisire, head of the country's Information Office, accuse Twagiramungu of being ineffective, and say he was lax about pursuing those who organized the killings last year of an estimated 1 million Rwandans, mainly Tutsis. ''Four months after the genocide, he was talking about four months being too long to follow up the perpetrators of the slaughter,'' Major Rutayisire says. ''What he was saying in effect was that too many Hutus are being arrested. He was not looking at them as criminals, but as Hutus, so he was sectarian in his outlook.'' But Eric Gillet, a Belgium-based representative of the International Federation of Human Rights Leagues, says the departing Hutu ministers were playing a critical role in moving Rwanda's government beyond its exclusive focus on the genocide and toward reconciliation. ''The Hutus who are departing were very much engaged in human rights defense and the idea of sharing power before the genocide,'' Mr. Gillet says. ''Their replacements will be Hutus who are much more under the control of [Tutsi] hard-liners,'' he adds. Last July, Tutsi-led rebels ousted a Hutu-dominated government accused of carrying out the four-month genocide and promised to build a multiethnic democracy. The new regime said it was ready to work with Hutu politicians who had not played a part in the genocide. The reshuffle throws that pledge into question. Government critics say the move shows Vice President and Defense Minister Paul Kagame and his allies in the new national Army are consolidating their power. Aid workers say if the government narrows its outlook and drums out its internal critics, international assistance to Rwanda could suffer. ''Although [foreign] money that has been pledged to the government isn't actually linked to the composition of the government, it will be an issue if the administration is seen as sliding in one direction,'' says one aid worker in Kigali. Many Rwandans had expected Twagiramungu's ouster. He and other outspoken Hutus have been increasingly marginalized in Rwanda's government, especially since they began openly criticizing the growing power of Rwanda's military and complaining that solders were abusing the human rights of the country's majority Hutu population. In June, one of the ex-prime minister's senior advisers fled to the Kenya's capital, Nairobi, after charging Rwanda's Army with persecuting Hutus. Rwanda's former chief prosecutor and treasury director also left the country after making similar accusations. In March, the governor of Rwanda's southern province of Butare, and a leading member of Twagiramungu's political party, was assassinated. Human rights monitors said extremist Tutsis were likely suspects. Twagiramungu's ouster strengthens the case of refugees in the sprawling settlements in Zaire, who argue that moderate Hutus have no power base in Rwanda. The more than 1 million refugees fled to Zaire last year, fearing reprisals for the genocide. One of the largest camps in Zaire is a crowded settlement called Katale that is home to more than 200,000 displaced. Many refugees there are Hutu professionals and intellectuals from Rwanda's capital Kigali. They argue that Rwanda's new Tutsi-dominated government encourages the return of villagers and farmers, but isn't interested in reconciling with educated Hutus who may question their policies. ''Intellectuals and young people are not welcome there,'' says a young man in a worn T-shirt who calls himself Eve. ''They want people that will submit easily,'' the former student argues. In recent weeks, Zaire's Army forcibly expelled about 15,000 refugees. It halted the effort last week, but has threatened to resume. Despite the threat of expulsions, the refugees haven't taken advantage of the United Nation's offer of an escort back home. Jean Epaule, another resident of the Katale camp, says he prefers to risk ill-treatment at the hands of Zairean soldiers in Katale than face persecution in Rwanda. ''You have to take into consideration the situation in Rwanda - the condition of justice, the composition of the Army. If it is the Tutsi army, then Hutu people can't go back. It's not an army for the people,'' Epaule says. The head of the United Nations High Commissioner for Refugees, Sadako Ogata, and Zairean Prime Minister Kengo wa Dondo were set to meet Aug. 29 in Geneva to discuss the future of the repatriations. If the talks fail, Zaire is likely to resume expelling the Rwandans at gunpoint. Since the UN effort to escort the displaced home voluntarily has foundered, the bargaining power the UN takes to the talks in Geneva has dwindled. UN officials began to evacuate all nonessential personnel from Goma, Zaire, as tensions in the region mounted after land mine and grenade explosions rocked Goma on Aug. 28. UN staff have been flying out of Zaire's airport in Goma, and many relief workers are scheduled to depart Aug. 30. The exit of the international aid workers is a setback to Zaire since the relief community injects much needed revenue into the region's economy. The UN's Ms. Ogata is set to begin a five-day tour of Rwanda, Burundi, and Tanzania on Aug. 30. Meanwhile, aid agency officials say Zairean Army officers are visiting some refugee camps to determine which ones to evacuate next. Relief workers fear any new expulsions will be violent.