PRISTINA, Yugoslavia (AP) _ Authorities proclaimed a day of mourning today for two police officers killed in bloody clashes in Kosovo province that left at least 21 people dead and 74 injured.

A spokeswoman for Kosovo's information office, Marija Gasi, told The Associated Press, ''Today the situation in Kosovo is normal. There has been no single extraordinary event.''

However, Radmilo Bogdanovic, interior minister of the republic of Serbia, described the situation as ''dramatic and changing from hour to hour.''

''The security forces are making great efforts to restore peace and order,'' Bogdanovic told Serbia's Parliament.

The protests in Kosovo, which is part of the republic of Serbia, began last week after Kosovo's Parliament approved constitutional changes giving Serbia control of the provincial police, courts and civil defense. Serbia's Parliament approved the changes Tuesday.

Ethnic Albanians, who make up 85 percent of Kosovo's 1.9 million citizens, say the changes threaten autonomy they won under the 1974 constitution.

Protesters hurled stones at riot police, who responded with tear gas. Two policemen, one an ethnic Albanian and one a Serb, were shot and killed Monday. Officials said 19 protesters died Monday and Tuesday.

Sources in Pristina, the capital of Kosovo, said there were unconfirmed reports two more demonstrators died during the night following clashes in the village of Zur, near the border of Albania.

Police in Zur shot to death an 18-year-old Tuesday, and the state-run Tanjug news agency reported 14 people injured in the village, which was sealed off by police.

The entire province was placed under an 8 p.m. to 5 a.m. curfew Tuesday.

Bogdanovic estimated that on Monday, the worst day of bloodshed and rioting, there were 14,000 mainly young ethnic Albanians on the streets of Kosovo, battling 2,400 police.

The Interior Ministry said 146 demonstrators were detained Monday and Tuesday.

There were rumors that several prominent ethnic Albanians, including businessmen, government officials and university professors, were questioned by police in connection with the violence. They could not be confirmed.

The deputy head of Pristina's university, Muhamed Bicaj, said he heard of one philosophy professor being questioned by police Tuesday night. The man was allowed to go home afterward, Bicaj said.

Serbia says the constitutional changes are needed to protect the province's Slav minority, which alleges harassment by ethnic Albanians. At least 30,000 Slavs are estimated to have left Kosovo since the last ethnic riots erupted there in 1981. At least nine people died in the protests.

The anniversary of those riots is Saturday. Officials hoped a heavy police presence in Kosovo, in addition to tanks and other military vehicles, would prevent new protests.

Tanjug said 76 people were injured in the latest unrest, two more than the figure released by the Interior Ministry.

According to the ministry, 25 policemen were injured - five seriously - and 49 demonstrators were hurt. It accused ethnic Albanian ''nationalists and separatists'' of fomenting unrest and sniping at police from buildings and rooftops.

There have been frequent allegations since 1981, particularly in Serbia, that Kosovo's ethnic Albanians have an organized underground movement that wants to unite the province with Albania. Ethnic Albanians deny such intentions.

In addition to the ethnic tension, Kosovo has been hard hit by the country's economic crisis. It is the poorest region of Yugoslavia, where inflation is expected to hit 400 percent in April and unemployment is 15 percent. In Kosovo, about 30 percent of the population is unemployed.

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