BELGRADE, Yugoslavia (AP) _ About 3,000 people staged peaceful anti-nuclear demonstrations in the Slovenian capital of Ljubljana on Thursday to mark the first anniversary of the Chernobyl nuclear disaster.

Eyewitnesses reached by telephone from Belgrade said the demonstrations began at the local student center, where children had painted the sidewalks with pictures of flowers and animals.

That was followed by an open discussion voicing anti-nuclear concerns and a march to the Slovenian parliament building.

There, demonstrators read out demands that included a call to close Yugoslavia's only operational nuclear power plant by 1991.

Anti-nuclear sentiments have been on the rise in Yugoslavia since the Chernobyl accident last year.

The nation's state-run media have sharply attacked government studies trying to determine locations for future nuclear plants.

Yugoslavia's only operating nuclear plant is at Krsko on the border between Croatia and Slovenia, where increasingly vocal youth groups have protested government policy on ecological and other issues since 1981.

The nation's national youth association proposed this week that nationwide referendums be held on any future nuclear projects in Yugoslavia.

Eyewitnesses said demonstrators in Ljbuljana carried a wide banner reading ''Lakes are dear to us - power plants are death,'' while others collected signatures calling for a referendum on the building of new nuclear facilities.

The demonstration was announced in advance to Slovenia's Communist authorities, which have shown increasing tolerance for such protests.

The demonstration occurred without incident or police interference, witnesses said.