Both sides said the number of dead was high, and each blamed the other for renewing hostilities.

"It's a bit too early for us to give specific casualties, but they have been very heavy," said Yemane Ghevreab, a spokesman for Eritrea.

Tensions have been rising along the border area in the last several weeks, despite efforts by the United Nations, United States, Kenya and other countries to stop a war that many outside officials worry could be particularly bloody.

Since a short burst of fighting ended last June, both nations have been buying tanks and warplanes and fortifying the border with thousands of soldiers. An estimated 200,000 or more troops are on the border.

A statement from the Ethiopian Government said that Eritrean soldiers attacked at dawn Saturday along one of three fronts, known as Badme-Sheraro.

The Ethiopians said that the attack was "successfully repelled" and that they captured the town of Geza Gerlase, which they described as a "major Eritrean stronghold."

Selome Taddesse, an Ethiopian spokeswoman, said the fighting did not include air attacks. The statement said Eritrean forces suffered heavy losses.

The Eritreans said that Ethiopian forces attacked them at 6 A.M., using tanks, artillery and missiles. Ghevreab said that he forces for the two sides are now roughly one mile apart, and that the attack failed to dislodge the Eritrean soldiers from their trenches but that many Ethiopians died in the attempt.

He said that 60,000 troops, on both sides, are in the immediate area.

He also said that no planes were used in the fighting but that the Eritrean Government warned people living in the capital city, Asmara, and other major towns not to go outside because of fear of air raids.

Eritrea, which had been the northern region of Ethiopia, became independent in 1993 after three decades of civil war. The two nations, both considered friends of the United States, never drew a formal line through the 625 miles that separate them.

A series of disputes largely over trade and economic issues exploded last year in a fight over sovereignty of the Badme region, a rocky and sparsely populated triangle that each side claims. Hundreds of people died, including civilians, in several weeks of fighting that ended in a cease-fire brokered by the United States.

In the last two days, Ethiopia has accused Eritrea of launching an artillery attack at the same front and of bombing the town of Adigrat. Eritrea strongly denied both accusations, saying that Ethiopia was looking for an excuse to begin fighting again.

The Organization of African Unity has proposed a peace plan, endorsed by the United Nations Security Council, that calls for Eritrea to withdraw its troops from the disputed border. Ethiopia has accepted the plan, but Eritrea has insisted it will not withdraw unless outside monitors are put in place.