BELGRADE, Yugoslavia (AP) _ Lawmakers in the central republic of Bosnia-Hercegovina decided today to hold a referendum on independence. But Serb members of Parliament walked out.

In Croatia, a 3-week-old cease-fire was generally holding, despite reports of minor violations.

Croatian defense officials said the federal army fired 15 mortar shells on villages near the Adriatic port of Zadar. They reported sporadic small-arms fire onto Croat positions near Sisak, 30 miles south of the Croatian capital Zagreb.

In a 16-hour session that ended early today, the Bosnian parliament decided to hold a referendum on Feb. 29 and March 1 on whether the republic should become an independent and sovereign state, the Belgrade-based Tanjug news agency reported.

Serb deputies walked out after protesting discussion of the issue. Parliament President Momcilo Krajisnik, of the Serbian Democratic Party, also left.

Serbs in Bosnia voted in a referendum earlier this month on the proclamation of an independent Serb state within Bosnia. Serb leaders in the republic have said they want to join a new, smaller, Serbian-dominated Yugoslavia.

The referendum in Bosnia could increase tensions. Serbs make up about one- third of the population of 4.3 million. Of the rest, about 43 percent are Slav Muslims and about 17 percent Croat.

So far, the civil war has been confined to Croatia, which declared independence in tandem with Slovenia last June 25. Fighting then broke out. Thousands of people were killed and Serb irregulars and the federal army captured one-third of Croatian territory.

But if conflict were to spread to Bosnia, analysts say it could be far worse.

Croatia and Slovenia have been recognized by the European Community and two dozen other nations. Bosnia and Macedonia also asked for recognition, but only Bulgaria has recognized those two republics.

The EC said it would recognize Bosnia only if all citizens voted in a referendum on independence.

Tanjug quoted unidentified Serb deputies in the Bosnian parliament as saying that Serbs would not take part in the referendum.

The U.N. undersecretary-general in charge of U.N. peacekeeping, Marrek Goulding, was to arrive in Belgrade on Sunday to discuss the deployment of peacekeepers. He was to meet with leaders in Serbia as well as leaders of Serb regions in Croatia which have declared themselves autonomous. Goulding is then to travel to Zagreb to confer with Croatian officials.