BELGRADE, Yugoslavia, Nov. 3— Pro-Serbian Yugoslav Army forces attacked the besieged Croatian town of Vukovar today with the apparent aim of capturing it before a Tuesday deadline set by the European Community for Serbia to accept a peace plan or face sanctions.
At the same time, advancing Croatian units routed Serbian irregulars from eastern villages between the towns of Daruvar and Slavonska Pozega in Croatia, prompting as many as 20,000 Serbs to flee, Yugoslav press agency reports said. Some accounts asserted that Croats had burned more than 25 villages populated by Serbs in the region. The reports could not be confirmed.
The fighting today, which also included artillery exchanges in Karlovac, Osijek and other towns, was described as the fiercest since the latest cease-fire accord was reached on Oct. 19. A dozen federal air strikes have been reported on targets across Croatia's eastern panhandle.
The clashes between Croats and the Serbian-dominated national army began about four months ago, shortly after Croatia issued an independence proclamation on June 25. Pressure on Peace Plan
Yugoslav analysts said the fighting this weekend might be part of a move by pro-Serbian officers in the army to sabotage the European Community's peace plan. Serbia has been under heavy pressure from the Europeans to sign the accord, which provides for the creation of a community of six sovereign republics and protection of the rights of ethnic minorities.
Serbia has so far resisted the pressure, arguing that ethnic Serbs in other republics, particularly Croatia, and the areas in which they live must be allowed to remain part of Yugoslavia.
A significant number of officers and leaders of the ethnic Serbs in Croatia and in another Yugoslav republic, Bosnia and Herzegovina, also oppose the European plan, preferring the notion of creating a rump Yugoslavia that would amount to a Greater Serbia.
Although the Serbian republic's government, headed by President Slobodan Milosevic, has pressed the proposal for a rump state, the effort would inevitably touch off economic sanctions, leading to social dislocation and further violence. There are signs that some high-ranking officials in the Serbian republic may favor signing the document, at least to buy time.
Serbia is expected to give its answer to the European Community at peace talks on Tuesday in The Hague. All of Yugoslavia's other republics have expressed willingness to go along with the European plan. Limits of Peace Accord
A Western diplomat in Belgrade pointed to the difficulties of enforcing a peace proposal in any case. "Frankly, what difference does it make if they all sign and the army is raging out of control?" the diplomat said.
Gunfire echoed today from the mountains above the Croatian resort city of Dubrovnik, which was heavily shelled on Friday and Saturday. Federal and Serbian forces surrounding Dubrovnik continued to warn that they would not end their siege of the the city until Croatian forces there withdraw.
Croatian defenders in Vukovar, which has been reduced to near-rubble by months of bombardment, appeared to be on the verge of collapse, local radio and news agency reports said. But it was unclear whether the Serbs' advance on Vukovar has been as successful as reports from both sides indicate.
Map of Yugoslavia showing location of Vukovar
