BELGRADE, Yugoslavia (AP) _ He was called the ''greatest son of our nations and nationalities'' while he ruled Yugoslavia. But on the 100th anniversary of his birthday Monday, Josip Broz Tito's country and his reputation largely were in ruins.

Tito's tight grip kept Yugoslavia together from the end of World War II to his death on May 4, 1980. May 25 was celebrated for 35 years as his birthday.

His slogan - ''the brotherhood and unity of all Yugoslavs'' - was an illusion that shattered upon his death. The federation has now split into at least four countries, and civil wars have killed more than 12,000 people and created more than 1 million refugees.

On Monday, his widow, Jovanka Broz, visited his grave in Belgrade.

Some citizens said they could recall nothing positive in what he did. Others found nothing positive in the years since he died.

''While he was alive, we had everything,'' said Rusmir Kapetanovic, a miner from the Bosnian town of Tuzla. ''And most of all, we had peace.''

But Stojanka Misic of the Serbian town of Leskovac spoke for many in telling Borba, the Belgrade daily: ''I would cut him into pieces and throw them to the dogs.''

Tito successfully led his Partizan guerrilla fighters through World War II, took power in Yugoslavia and then led his Communists to rule unchallenged for 35 years.

He clamped down on any nationalist dissent, especially in his native Croatia and in Serbia, the two biggest republics.

Now, Serbian ultra-nationalists have threatened to mine his grave in the Dedinje district of Belgrade, and some Serbian politicians have said his body should be returned to Croatia.

All eight towns in the old Yugoslavia that had taken Tito's name have changed it. The capital of Montenegro, called Titograd, reverted to Podgorica.

Belgrade's main street, Marshal Tito Street, was recently renamed the Street of Serbian Rulers.

''Tito's era of dictatorhip is gone,'' said Radovan Jovic, a student from Bijeljina. ''But other dictators have taken his place.''

Ethnic fighting, which started after Slovenia and Croatia declared independence last June 25, began the breakup of the former federation. Those two republics and Bosnia-Herzegovina have been admitted to the United Nations.

A fourth republic, Macedonia, still is waiting for international recognition, leaving only Serbia and its tiny ally Montenegro in what was Tito's Yugoslavia.