The two biggest Eritrean querrilla organizations called yesterday for direct negotiations with Ethiopa's Marxist military rulers to end 17 years of war for the independence of the Red Sea province of Eritea.

They said, however, that the negotiations must accept "the right of self-determination for the Eritrean people," a condition that, in the view of Western observers, will make the offer unacceptable to the Ethiopian government.

The call was issued at a joint press conference here by Ahmed Nasser, head of the Eritrean Liberation Front-Revolutionary Council (ELF-RC), and Ramadan Mohammed Nour, secretary general of the Eritrean Peoples Liberation Front (EPLF).

The joint statement was said to mark the effective merger of the two rival nationalist organizations into a joint political command.

It came a week after Nasser's return from a secret 10-day visit to Moscow amid signs of increased Soviet pressure for a negotiated end to the war in Eritrea, a strategic area with a 600-mile coastline on the Red Sea.

The EPLF had agreed on June 21 to seek peace talks, the press conference was told, because they felt that continued fighting was in the interests of neither the Ethiopian nor the Eritrean people.

Members of the ELF-RC leadership at the press conference said there was no direct link between the call for negotiations and Nasser's visit to Moscow, the first by an Eritrean leader.

But sources in close touch with Soviet foreign policy said the call reflected the desire of the Soviet Union and tis Cuban allies to bring the Ethiopian leadership and Eritrean guerrillas to the negotiating table.

The Soviets are understood to favor a confederation between Ethiopa and Eritrea, a solution they believe would give them access to the Red Sea ports of Massawa and Assab, Ethiopia's only outlets to the sea.