MADRID, Spain (CNN) -- The incumbent Basque nationalists won the most seats in Basque regional parliamentary elections on Sunday, but they could lose a 29-year hold on power because three non-nationalist parties won a combined majority for the first time, according to official election results.
Socialist candidate Patxi Lopez speaks to reporters after voting Sunday in regional parliamentary elections.
The vote for the powerful 75-seat regional parliament and Basque president are seen as a bellwether of the region's sentiment on how to end decades of violence by the Basque separatist group ETA.
The moderate Basque Nationalist Party won 30 seats, and its traditional smaller party allies won seven more.
But the crucial 38-seat majority went to the Basque branches of Spain's ruling Socialist Party, with 24 seats; the conservative Popular Party, with 13 seats; and the new Progressive Union and Democracy party, with one seat, according to official results.
The Socialist candidate, Patxi Lopez, told supporters the vote "legitimized" his bid to "lead the change." Negotiations with other parties to make Lopez the next Basque president were expected in the coming days.
The non-nationalist parties have taken a forceful line on trying to end ETA's violence, blamed for nearly 800 deaths.
ETA stands for Euskadi ta Askatasuna, or "Basque Homeland and Liberty" in the Basque language. The group wants an independent Basque homeland, but is classified as a terrorist group by the European Union and the United States, because of car bombings and fatal shootings.
The Basque Nationalist Party seeks self-determination for the 2.1 million Basques but does not support ETA's violence.
Some 600 ETA suspects or convicts are in Spanish jails, and three alleged top leaders of the group were arrested last year. But ETA has continued to defy officials -- bomb attacks, including a major blast that damaged a construction company office in Madrid three weeks ago, continue to be attributed to the group.
For the first time, political parties linked to ETA were banned from running in the Basque elections. Spanish courts in recent years outlawed a leftist party called Batasuna, and others, saying they secretly and actively aided ETA. One such party holds nine seats in the outgoing parliament.
The incumbent Basque president and nationalist leader, Juan Jose Ibarretxe, scolded the Socialists and the conservatives during the campaign as being outsiders and puppets of their national offices in Madrid.
But Lopez, the Basque Socialist leader, accused the Basque nationalists of trying to divide the Basques, between those who favor self-determination and those who prefer to remain firmly a part of Spain.
The Basques want "dialogue and a change of course," Lopez said.
He has vowed to govern for all Basques, and Spain's Socialist Prime Minister, Jose Luis Rodriguez Zapatero, campaigned in the Basque region to support Lopez.
For years, Socialist and conservative politicians, even low-level town councilors, in the Basque region have been protected by police or private bodyguards due to ETA death threats. Several have been killed nonetheless. But this year, the Basque nationalist party also has come under ETA attack.
ETA violence is a regular feature of Basque and Spanish elections.
Earlier this week, a predawn bomb attributed to ETA heavily damaged a new Socialist party clubhouse in the Basque town of Lazkao. The next day, the son of a former Socialist councilman there allegedly swung a heavy mallet to smash the glass windows and damage a social club linked to leftist pro-independence supporters. That man reportedly has now fled the town.
An ETA statement on Friday, issued to the Basque newspaper Gara, called Sunday's elections "anti-democratic" and predicted they would result in a "fascist parliament."
Spain's economic crisis was somewhat less an issue in the relatively prosperous Basque region -- heavy on industry and services -- which still has slim economic growth and an unemployment rate of 8 percent, compared with the national average of nearly 14 percent.
The three-province Basque region, whose largest city is Bilbao, has extensive home-rule powers, including a regional police force that is involved in the fight against ETA, control of education and health care, and tax collection.
Elsewhere on Sunday, in Spain's northwest Galicia region, the opposition conservatives won a majority in the Galicia regional parliament. They will dislodge the leftist governing coalition, led by the Galicia branch of Spain's Socialist Party.
The defeat was seen as blow to Prime Minister Zapatero.