KHARTOUM, SUDAN, DEC. 9 -- The Eritrean separatist movement in northern Ethiopia claimed today that its forces have "smashed through" Ethiopian Army lines in what the rebels said was the largest battle in the region in the past two years.

Leaders here of the Eritrean People's Liberation Front (EPLF) said in statements that could not be verified independently that the fighting began early yesterday when rebel forces overran fortified Ethiopian government positions near the town of Nakfa, about 120 miles north of the Eritrean capital of Asmara.

If true, the rebel claims signify the outbreak of a full-scale war amid a severe food shortage and major international famine relief efforts in northern Ethiopia. More than 2 million people in the region are estimated to be faced with starvation.

Nakfa marks the front line in the 26-year-old war between Ethiopia and the rebels, who want to create a separate nation out of the former Italian colony of Eritrea. Both rebel and government troops are dug into trenches at Nakfa that have been held since 1978.

The rebels have used their trenches in the rugged mountains to block eight major Ethiopian offensives in the past decade. U.S. diplomats say those offensives have been waged with more than $3 billion in Soviet-supplied weaponry.

Rebel leaders in Khartoum said that their forces had killed 793 Ethiopian soldiers and captured 302 others. In past years, the Ethiopian government has refused to comment on events in the war, which is the world's longest-running civil conflict.

Osman Mohammed Omer, a member of the rebels' ruling central committee, said here that the Nakfa fighting marks the beginning of a major offensive to push Ethiopian troops, estimated by western sources to number about 120,000, out of Eritrea. The rebels are believed to have about 30,000 soldiers, about half of whom are deployed on the front lines.

"Now we have reached the stage where we can take the initiative and beat back the Ethiopian government troops," Osman said. Western analysts have said for several years that the Ethiopian government, despite its larger army and modern Soviet weapons, appears incapable of dislodging rebel forces from their fortified mountain positions. But they also have said that the rebels do not have the firepower to force government forces out of the region.

This week's reported offensive coincides with severe drought and widespread food shortages in northern Ethiopia. The region is being criss-crossed by convoys carrying relief food, moving both in government and rebel-held areas.

Large numbers of peasant farmers in Eritrea and nearby Tigray have run out of food and are reported by relief officials to be walking toward Sudan.

"An EPLF offensive at this time might force the Ethiopian government to hit concentrations of civilians in reprisal especially, if the Ethiopian government forces are being routed," said one senior western relief official here.