ZAGREB, Croatia (AP) _ Four weeks ago, a Croatian soldier broke into Nada Radisic's apartment, changed the locks and moved in. Her only offense was marrying a Serb 13 years ago.

''I am desperate,'' Mrs. Radisic said, sitting with other women in the apartment across the hall.

At the Serbian Orthodox Church, 60-year-old Ruzica Madjarac sat in the priest's office crying. Her sister's apartment in Karlovac has been seized by strangers and her state pension cut off.

''I can't change my parents. I cannot change who I am,'' cried Mrs. Madjarac, an ethnic Serb who has lived in Zagreb 36 years.

In a country where ethnicity means everything, ethnic Serbs and Croats married to them are suffering what some contend is widespread discrimination and harassment.

As in cases of alleged Serb harassment of Croats, proving a pattern is difficult. But stories of evictions or destruction of homes, threatening phone calls, job dismissals and legal limbos make their way regularly to U.N. officials in Croatia.

''There is a problem everywhere in Croatia,'' a top U.N. official said.

The official, who spoke on condition he not be further identified, said he knew of Serbs in Zagreb who'd lost jobs or been told to leave their homes. Serbs trying to return to their homes in former battle zones have been detained by local and military police, he said.

The dynamited remains of Serb-owned houses dot the towns of Daruvar and Pakrac. Unconfirmed media reports say as many as 6,000 Serb houses in Croatia have been intentionally destroyed.

Serb political and religious leaders say thousands of Serbian school children are being given Roman Catholic education to hide their ethnicity.

''You can't say it's force, but you can't say it's free will either. Pressure is the word,'' said Zarko Puhovski, professor of political philosophy at Zagreb University and a Croat.

Milenko Popovic, acting head of Zagreb's Orthodox Church, contends Croats are conducting their own form of ''ethnic cleansing,'' forcing out a minority to create ''pure'' areas.

Tadeusz Mazowiecki, the U.N. Human Rights Commission special envoy, said ethnic cleansing was being ''implemented in Croatia ... but in a more subtle way'' than in Serb-controlled areas.

Mazowiecki's report on human rights abuses in former Yugoslavia is expected Monday.

In Zagreb, the Serbian Democratic Forum, an advocacy group for Serbs in Croatia, and the orthodox Church of the Holy Transfiguration have become way- stations for Serbs with nowhere else to turn.

As Popovic described the complaints of the approximately 10 Serbs he sees daily, a young man entered his office, eyes wide with terror.

The Bosnian Serb, a 10-year Zagreb resident married to a Croat, had been drafted by the Croatian Army, though not granted citizenship, and threatened with arrest if he didn't report. He fears meeting his brothers, still in northern Bosnia, on the battlefield.

''I'd rather kill myself than risk killing my brothers,'' said the 33-year- old man, his hands trembling.

Milos Stojic, a 55-year-old Karlovac resident, now sleeps in train stations or with friends.

The former math teacher, who suffers from epilepsy, said that while he was hospitalized late last year, men broke into his apartment, ransacked it and Croats later moved in.

''Serbs have lived here hundreds of years, and it's our homeland as well,'' said Stojic.

''It's not just losing national identity, it's sort of a pogrom on Serbs who did not take part in the armed rebellion,'' said Petar Ladjevic, the forum's secretary-general.

Mrs. Radisic and Mirjana Danilovic, her 52-year-old neighbor who's also been threatened, feel the same. Both women's husbands fled with Yugoslav Army troops when they abandoned their Zagreb barracks last year during fighting between Croatian troops and rebel Serbs.

Mrs. Radisic and her daughter were on vacation when the man and three colleagues, all in military camouflage, broke in July 25.

Her neighbors notified local and military police, and Mrs. Radisic has since spent countless hours shuffling between government offices, so far with no luck.

Taped to the door of her apartment is a white piece of paper with, ''Zdravko Magdic, HV,'' identifying the new tenant as a member of the Croatian Army.

''One of Magdic's colleagues asked me if I was familiar with the law,'' said Mrs. Radisic. ''I said a bit. He said, 'Then you know that in practice there is no law in existence except the law of weapons.'''