BELGRADE, Yugoslavia (AP) _ People in Yugoslavia's largest republic voted Sunday on whether to hold free elections before adoption of a new constitution that would give it more power over a southern province.

Turnout was light on a hot Sunday morning in Belgrade, which serves as both the seat of the federal government and the capital of the Serbian republic. Voting will continue Monday, and results are to be released Tuesday.

Serbian Communist President Slobodan Milosevic announced the referendum June 25 for Serbia, the largest of Yugoslavia's six republics.

It was preceded by a barrage of propaganda in the state media calling on voters to support a delay in free elections until after enactment of a new constitution, for which no date has been set.

Serbia's Communist authorities in the past have rejected Western-style pluralism.

The northern Yugoslav republics of Slovenia and Croatia, in contrast, held the first free elections this spring in 45 years for local legislatures. Both elections were won by center-right parties, which trounced the Communist parties that called the elections.

Yugoslavia's other three republics are scheduled to hold free elections later this year.

Milosevic claims that multiparty elections cannot be held in his republic because ethnic Albanians, who make up 90 percent of the 1.7 million inhabitants of Serbia's southern Kosovo province, will vote for separatists advocating the region's secession.

At least 60 ethnic Albanian protesters have been killed since February 1989, when the republic set strict limits on Kosovo's autonomy and demonstrations resulted.

The possible elimination of the Kosovo parliament through a new constitution would make ethnic Albanians a small minority in the Serbian parliament. Ethnic Albanians do not necessarily want independence, but do want their previous partial autonomy restored.

The ethnic Albanians seek restoration of the broader autonomy they enjoyed under a 1974 constitution that was amended in March 1989. Serbia said the changes were needed to protect the Serbian minority in Kosovo from alleged harassment by ethnic Albanians.

The Serbian parliament previously adopted unspecified new powers to amend measures passed by Kosovo's administration in a further extension of Serbian control.

Serbian Communists claim full ethnic Albanian autonomy is the first step toward Kosovo seceding from Yugoslavia and joining neighboring Albania.

A coalition of Serbian opposition parties, described as ''national traitors'' by the government media, have insisted Kosovo's problems have been caused by the ruling Communists and that they can only be resolved after a democratically elected government takes over in Serbia.

Opposition leaders were attacked and beaten by police when they tried to stage a protest in front of Belgrade Television to demand equal access to the media.

No opposition representatives were present at any of the voting stations visited by a reporter, but Communist officials claimed they would be allowed to observe the proceedings if they wished.

Ethnic Albanian leaders in Kosovo have called on people in Kosovo to boycott the referendum.

''Nothing can be decided without Albanians in Kosovo anymore,'' said Azem Vlasi, a former Communist leader in the province, said in an interview with the Nedelja weekly.