SARAJEVO, Bosnia-Herzegovina (AP) _ A senior U.N. officer said Saturday that an initial investigation indicates an Italian relief plane was shot down by ground-to-air missiles outside Sarajevo.

But an Italian air force general investigating the crash said although he could not rule out a missile hit in Thursday's crash, the probe could take months. The plane's four crewmen were killed and all relief flights were suspended.

In the Bosnian capital, heavy rain and cold, blustery weather quieted the big guns on Saturday, but Bosnia's government said Serbs were using water and electricity cutoffs as new weapons against the city's residents.

Fighting flared elsewhere in Bosnia-Herzegovina. Bosnia's Health Ministry said for the 24-hour period ending at noon Saturday, 20 people had died and 182 were wounded republic-wide, including six dead and 79 wounded in Sarajevo.

More than 8,000 people have died - some estimates say up to 35,000 - and tens of thousands are missing in Bosnia's civil war, which began after Muslims and Croats voted for independence from Serbian-dominated Yugoslavia. An estimated 2 million people are refugees.

The senior U.N. officer, who spoke on condition of anonymity, said according to an initial investigation, two missiles - either Stingers or Strelas - were used to shoot down the relief plane. Strelas are the Yugoslav versions of SAM-7 ground-to-air missiles.

Previously, Western officials have said there was evidence the twin- turboprop transport may have been downed by an anti-aircraft missile.

The U.N. officer, who visited the mountainous crash site southwest of the city, told The Associated Press that missiles hit the plane as it was between 4,000 feet to 6,000 feet and descending toward Sarajevo's airport. He said one missile hit the engine, which explained why part of it was found far from the main crash site.

Brig. Gen. Luciano Battisti, chief of flight safety for the Italian air force, said if the plane was indeed shot down, a ''man-portable, infrared missile'' was used. He called for an investigation to determine which party in Bosnia's conflict possesses such a weapon.

Troops of Bosnia's Muslim, Croat and Serb factions all operate around the area where the Italian plane crashed. Serb and government officials have blamed each other.

Battisti, who spoke at Sarajevo's airport, where U.N. soldiers loaded four body bags with the crews' remains onto a C-130 transport plane, said he was bringing pieces of the plane to Italy for investigation. The biggest piece was about 6 feet long and appeared to be part of the turboprop.

The U.N. airlift to the besieged Bosnian capital was suspended after the crash. In Geneva, the chairmen of a peace conference called for an emergency meeting of the warring parties in to discuss a resumption of humanitarian relief flights.

The airlift, which has so far delivered about 1,000 planeloads of food and aid, is considered vital for the survival of Sarajevo's 400,000 remaining inhabitants.

In a related development, the United Nations' top peacekeeping official said the U.N. secretary-general would recommend to the Security Council a ''considerable enlargement of both the mandate and the strength'' of U.N. forces in Bosnia.

The official, Marrack Goulding, in the Croatian capital of Zagreb, said U.N. peacekeepers could provide military escorts to humanitarian land convoys or use military trucks and drivers to deliver the goods themselves on especially dangerous routes.

He said a decision about new ground troops was ''very urgent,'' but that there were no immediate plans for military planes to escort relief flights.

There are about 15,000 U.N. soldiers deployed in Croatia and Bosnia- Herzegovina. Goulding did not say how many additional troops he would recommend.

In Sarajevo, water pressure dropped or taps ran dry in the few parts of the city that still have running-water supplies, and Bosnian officials accused Serb militiamen, who control the main reservoir outside the Bosnian capital, of cutting back the supply. The government side also said the Serbs had switched off two electrical stations outside the city.

Yusuf Khalef, chief spokesman for the U.N. protection force, said talks between the two sides on water and electricity were scheduled for Sunday.

Elsewhere in Bosnia, the Belgrade-based news agency Tanjug said five people died and several were injured when Bosnian government forces shelled Teslic, 54 miles northwest of Sarajevo. Tanjug also reported heavy fighting throughout northern Bosnia, near the Sava River, and in Jajce, a central town.