Rwanda Rebels, Army Trade Mortar Fire : Africa: Fighting blocks relief supplies. U.N. officials warn of food and medical shortages.

Rwanda’s battered army in Kigali regrouped Wednesday and exchanged heavy mortar fire into the evening with rebel guerrillas who captured a strategic government position in the capital two days earlier, U.N. officials reported.

The fighting, which shattered a truce declared for the visit of a senior U.N. envoy, again prevented relief supplies from being flown into the capital, and the U.N. officials expressed fears that shortages of food and medicine had become critical.

One of the mortar rounds, apparently fired by rebels of the Rwandan Patriotic Front, hit a Red Cross hospital in the government-controlled section of Kigali, killing two Rwandan nurses, the officials said.

Rebels also pounded army positions near the Defense Ministry, while the army lobbed shell after shell on rebel forces on the outskirts of the city.

On Monday, the Tutsi-dominated rebels--who say they are fighting a war of liberation against the predominantly Hutu government--had mounted a three-pronged attack and captured the Kanombe army camp overlooking the airport. The three battalions of defenders fled, and some diplomatic observers in Nairobi believed that the rebels would soon win the battle for Kigali.

But in other African wars--in Liberia, Angola and Somalia, for example--armies that may have wilted in the countryside have been willing to fight fiercely to defend their capitals.

The reason is particularly clear in Rwanda: The government, the military, communications and transportation facilities are centralized in the capital; without the capital, the government would have little left worth fighting for.

The fighting Wednesday further delayed the arrival of a 5,500-member, all-African peacekeeping force under U.N. command.

The United Nations’ special envoy, Iqbal Riza, is in Kigali trying to persuade both sides to allow deployment of the troops and the United Nations to take control of the airport.

But Riza’s talks may be premature because only three African nations--Ethiopia, Ghana and Senegal--have agreed to participate in the force. Their commitment totals 2,200 soldiers.

Riza traveled in an armored vehicle through the fighting on the western edge of the city to the seat of the interim government in Gitarama, 25 miles southwest of Kigali.

The Associated Press reported that he hoped to hold talks today with the rebels in Mulindi, a rebel stronghold just south of the Ugandan border.

Western diplomats in East Africa are not optimistic about the chances for a lasting, negotiated political settlement, because rebel commanders appear to want nothing less than a military victory that will put them in position to bargain for a large share of power, even though the Tutsis are 9% of the population.

At the same time, most moderate government officials who favored conciliation between the majority Hutus and minority Tutsis have been killed, and the surviving officials now at Gitarama represent the extremist wing.

This element appears to support the eradication of the Tutsis and is widely believed to be responsible for the widespread massacres that have claimed the lives of at least 200,000 Rwandans, most of them Tutsis, since April 6.

The fighting is slowly turning Kigali into a ghost town and is depopulating the countryside.

The United Nations has set up 15 camps in neighboring Tanzania, Uganda and Zaire for the estimated 2 million Rwandans who are now homeless.

In Benaco, a Tanzanian refugee camp that holds 300,000 Rwandans, Red Cross workers Wednesday reported the first six cases of meningitis, an easily spread bacterial disease that can be deadly.