SARAJEVO, Bosnia-Herzegovina (AP) _ Serb gunners attacked Sarajevo's southern defenses Friday in a 3 -hour bombardment that put the city on general alert.

There were no immediate reports of casualties during the attack, in which Bosnian army positions in the Trebevic and Zlatiste areas came under heavy tank, artillery and mortar fire.

The southern defense lines are under new command after the arrest this week of two renegade Bosnian army officers on criminal charges. The barrages targeted neighborhoods that the officers had run like personal fiefdoms.

Army officials contend that the command turmoil has not jeopardized Sarajevo's defenses, which appeared to be holding. But Serbs who have besieged the Bosnian capital for 18 months seemed intent on testing them.

The same neighborhoods were hit Thursday when at least 750 shells rained down on Sarajevo's front lines, ''an unusually high number,'' said Cmdr. Idesbald van Biesebroeck of the U.N. peacekeeping force in Sarajevo.

Government-run radio said the city was on general alert Friday to warn citizens of possible danger from shelling or other hazards. An alert is usually taken to mean that citizens should not leave their homes unless absolutely necessary.

One of the arrested army officers, Musan Topalovic, was shot to death trying to escape early Wednesday, the government said. The other, Ramiz Delalic was in custody.

Elsewhere, Bosnian radio said nine Muslims were killed in a mortar attack on the northern Bosnian town of Maglaj. The report could not be confirmed independently.

Bosnia's war broke out 18 months ago when the republic's Serbs, who now hold 70 percent of Bosnia, rebelled following a vote by Muslims and Croats independence from Serb-dominated Yugoslavia. As many as 200,000 people are dead or missing.

In other developments Friday:

- U.N. troops continued probing the charred remains of a mountain village 20 miles north of Sarajevo, where Bosnian Croat forces are accused of massacring Muslims last weekend. At least 25 bodies have been recovered. Some houses north of the village were reported in flames, and U.N. troops feared more violence.

- The head of a U.N. team investigating war crimes in former Yugoslavia said he will meet with Serb leaders in Croatia on Saturday to try to clear the way for the excavation of a suspected mass grave near the western Croatian city of Vukovar. Serbs had stopped a forensic team organized by the Boston- based Physicians for Human Rights from beginning exhumations on Oct. 19.

- Fighting eased between Muslim-led government forces and soldiers loyal to a local Muslim leader in the Bihac area of northwestern Bosnia, which declared autonomy Sept. 27. U.N. officials said about 20 people were injured in fighting Thursday.

- Foreign Minister Haris Silajdzic was confirmed as prime minister and new ministers were named to handle ''coordination'' with the districts of Tuzla, Zenica, Bihac and Mostar. The changes apparently are intended to consolidate support for President Alija Izetbegovic.

- The European Community rejected immediate use of military force to get humanitarian aid into war-torn Bosnia, but agreed more money and troops should be sent to protect aid convoys. The United Nations suspended its aid convoys to central Bosnia after the death of a Danish aid worker earlier this week.