Serbs, Croats Battle; Army Is Drawn In : Yugoslavia: Ethnic fighting takes lives in Croatia. Leaders, meeting with European envoys, agree to start talks Aug. 1 on the conflict.

Fighting erupted in several villages of northeastern Croatia on Sunday, pitting Serbs against Croats and drawing the federal army into a long-feared bloodletting that raged for at least 10 hours.

Reports of casualties were contradictory, with the Yugoslav news agency Tanjug saying four were killed and Croatian authorities claiming the death toll was in the dozens.

Belgrade Television showed ambulances screaming into the village of Tenja, where tanks and bullet-riddled cars were abandoned on the roadsides, houses smoked from mortar fire, blood was spattered on the sidewalks and at least two corpses lay on the main road.

Later Sunday, leaders of Yugoslavia and of its constituent republics accepted a European Community peace plan after negotiations on the Adriatic island of Brioni.

News service reports from Brioni said that negotiators, including three EC foreign ministers acting as mediators, agreed that all parties will begin talks Aug. 1 on every aspect of the future of Yugoslavia in an effort to avert the current threats of civil war and disintegration.

The talks will take place during a three-month moratorium by the breakaway republics of Slovenia and Croatia of further moves to implement their independence declarations of June 25, according to Foreign Minister Hans van den Broek of the Netherlands, one of the EC mediators.

Van den Broek said that under the plan, the EC will, as soon as possible, send a small group of civilian and military observers to monitor the current cease-fire between Slovenian forces and the Yugoslav army. The team would monitor fulfillment of all other aspects of the agreement, he said.

The accord, he added, also provides for the federal presidency to re-establish full control over the Yugoslav armed forces and for the return of all federal and Slovenian armed forces to their bases by midnight tonight (3 p.m. PDT).

The violence in Tenja and other ethnically mixed villages about 100 miles west of Belgrade followed warnings a day earlier by both Serbia and Croatia that a bloody civil war loomed over the deeply divided Balkan federation.

The deadly clashes shifted the focus of Yugoslavia’s escalating conflict to Croatia after more than a week of attempts to firm up a cease-fire in Slovenia, where 60 were killed and 300 wounded in battles with the federal army last week.

The four-day-old cease-fire appeared to be holding in Slovenia.

Slovenia had been ordered by the federal presidency to turn over control of its 27 international border crossings to Yugoslav authorities by noon Sunday. It steadfastly refused to do so, claiming control of the frontiers has always been a matter for the republics, not the federal government or the army.

News reports from Brioni said the accords reached there late Sunday included a compromise agreement, giving Slovenia partial control of its border posts.

The Croatian head of the collective presidency, Stipe Mesic, has said the ruling body will not resort to force to wrest the border stations from Slovenia.

However, the army has been deploying troops and issuing threats on its own, without presidential authority, raising the question of whether Mesic actually wields much influence over the Serbian-dominated military.

The federal Defense Ministry in Belgrade accused Slovenia of “treacherous conduct” in a virulent report on alleged humanitarian violations. While the military claims appeared exaggerated, their airing shortly after the deadline expired for Slovenia to hand over the border stations sparked fears of another military strike against the breakaway republic.

In northeastern Croatia, fighting broke out in Tenja and in other villages around Vukovar and Osijek after Croatian reservists moved in to rout Serbian extremists known as chetniks.

Croatian media claim that hundreds of chetniks have infiltrated their republic to help local Serbs in their armed struggle against Croatia’s secession from Yugoslavia.

Both Slovenia and Croatia declared their republics independent of the crisis-torn federation on June 25.

Tanjug said that gun battles raged between Serbs and Croats for 10 hours. The report indicated a cease-fire had been arranged but gave no details. It also gave little information about the federal army’s role in the fighting.

Federal troops and tanks of the Yugoslav People’s Army moved in to Serbian-populated regions of Croatia and Bosnia-Herzegovina on Wednesday, only a few hours after the chief of staff issued a menacing statement that many thought signaled a behind-the-scenes military coup d’etat.

Gen. Blagoje Adzic, an arch-conservative Serbian Communist, vowed to crush Slovenia’s moves toward independence, although tanks and troops have been deployed elsewhere.

Adzic’s ominous threat to deliver “a massive and rigorous military strike” against Slovenia has not yet been explained. It intensified speculation that the army has engaged in renegade behavior, since no federal authorization was given for the 180-vehicle deployment of heavy armor and the federal Defense Minister has distanced himself from threats of a strike.

Tanks and troops deployed to the volatile region of northeastern Croatia moved into Tenja after clashes broke out between Serbs and Croats, and media reports indicated that the fighting intensified after the army intervened.

Zagreb Radio quoted the mayor of Osijek, Zlatko Krmaric, as saying the army was supporting rebel Serbs.

“The army has again sided with the chetniks who have been shooting at the national guard from behind armored vehicles,” the mayor complained in the broadcast.

Krmaric said there were “many injured and dead” among the Serbian nationalists, and a spokesman for the Croatian Defense Ministry in Zagreb made the same claim.

“We think that there must be dozens of dead people,” the spokesman, Mate Salinovic, told reporters in the Croatian capital.