Almost a year after the Spanish government and Basque nationalists struck a historic bargain that paved the way for autonomy in the strife-torn northern provinces, violence has increased, divisions in the Basque country are sharper and a bomb campaign aimed at the nation's lucrative tourist industry has again put the separatist organization ETA on Europe's front pages.

According to Juan Tomas de Salas, publisher of Spain's leading news weekly, Cambio 16, "Our democracy has only got one frontal enemy and that enemy is called ETA." Other Spanish commentators see the separatist gunmen and bombers as only a symptom and point to a more general breakdown of the social fabric in the Basque country.

A Basque nationalist congressman said a year ago that achievement of the agreement on autonomy was like catching "the last coach on the last train to peace" in the Basque homeland. Officials of the central administration and Basque politicians now agree, however, that catch phrase was too optimistic.

In the first six months of the year, 57 persons died in Basque-country violence. Half a dozen other assassinations elsewhere in Spain put the total figure above 60, which is three times the dead over the same period in Italy, with its Red Brigades and neofascists, and in excess of the dead in Northern Ireland.

While the majority of the killings have been the work of the ETA, whose initials in Basque stand for Euscadi ta Askatasuna (Basque Homeland and Liberty), an onimous sign in the recent violence has been the onset of straight sectarian violence, with extreme right-wing groups carrying out reprisal bloodlettings.

Last weekend in the city hall of the Basque city of San Sebastian, about a hundred senior members of the powerful Basque Socialist Party staged a sit-in. Among them were senators and coangressmen of the national parliament as well as representatives of the Basque autonomous parliament. They were protesting recent killings in the area, for which ERA claimed responsibility, and attempting to rally other political parties in a joint condemnation of terrorism.

Underlining the instability of the region was a takeover of the Basque parliament June 2 by about 600 laidoff steelworkers who stormed the assembly building in the main industrial city of Bilbao and held the Basque autonomous government and members of the assembly hostage overnight. The direct-action line adopted by the workers was termed by Carlos Garaikoetxea, president of the Basque automonous government and of the majority Basque Nationalist Party, "an assault on democracy" whipped up by "predatory birds and carriers of carrion."

Garaikoetxea's outburst came at a press conference after he had persuaded the demonstrators to leave. The former businessman had negotiated Basque autonomy last July after a series of marathon disucssions with Spanish Premier Adolfo Suarez. The workers were led by Basque nationalist radicals, who seek creation of a workers' republic in the Basque country. They are closely allied to the terrorist ETA groups currently placing bombs along Spain's tourist-packed Mediterranean coastal resorts.

Autonomy was endorsed by a narrow majority on a referendum last October in the Basque proviences but it was rejected out of hand by the ETA radicals. ETA termed autonomy a sellout to the national administration and announced continuing struggle for an independent Basque republic.

In March elections to the autonomous Basque parliament, the political from organization of the hard-line military wing of ETA emerged second only to Garaikoetxea's more moderate and accommodating Basque National Party.

ERA's bomb blasts at coastal resorts do little damage and coded ETA phone calls warn the police to clear the target areas. The intention, according to Commerce and Tourism Minister Luis Gamir, is "not to kill or maim tourists but to scare them away."

Some 38 million visitors came to Spain last year, spending $6.4 billion.

So far there has not been firm evidence of the blasts leading to cancellations on a large scale but hoteliers readily admit that should the blasts continue, the effect could be disastrous. A similar bombing campaign last year is at least partially blamed for a drop in visitors of 9.3 percent during the first five months of 1980 compared to 1979.

The bomb campaign aims to force the release of 19 ETA prisoners, the replacement of the governor of Soria Prison, where most ETA suspects are held and steps to incorporate into the Basque country the disputed border province of Navarre. It is 50 percent ethnically Basque. The demands have been rejected outright by the central government with the full backing of opposition parties.

About 300 Basques are held on charges ranging from murder to armed robbery. Demonstrations by radical Basque groups demanding "amnesty" can turn into violent riots. In San Sebastian recently, demonstrators were attempting to block the main Madrid-Paris railway line. Surrounded by police, the demonstratoros broke through the cordon by lobbing a gasoline bomb into a police vehicle. Five security agents were severely burned.

According to Spanish commentators, there is a growing division in Basque politics between the mainstream Nationalist Party, which backs home rule within the framework of a federal state, and those who are broadly behind ETA and participate actively with the separatist organizations on such issures as annesty for prisoners.

Complicating the problem is the fact that the majority Basque Nationalist Party, Catholic and conservative, is itself at odds with the centrist government of Suarezx despite close ideological links. While a year ago Garaikoetxea and Suarez were able to break a historic deadlock between Madrid and the Basque country on the basis of personal contact, the Basque Nationalist Party has boycotted the national parliament this year. It alleges breach of faith on the extent and pace of the transfer of powers to the autonomous Basque government and assembly.

Behind the Basque nationalist boycott lies the fear of being outflanked politically by the radicals. The Madrid administration is concerned that it is politically unacceptable for the rest of Spain to meet immediatiely all the Basque home-rule demands. The government is attempting to slow the pace of autonomy in all regions.

Against the background of the bombings on the coast -- there were nearly a dozen bombs in tourist resorts in the first week of the ETA campaign -- the police in the Basque country have cracked down on radical politicians. Three members of the Basque Left, a communist-nationalist group with growing electroal support, were arrested under an antiterrorist law that allows suspects to be held for 10 days without access to lawyers. Charges were believed to be related to the bombs on the resorts.

The leader of the Basque Left coalition, Mario Onaindia, termed the arrests "a very grave provocation" against the Basque people. Onaindaia, himself a former ETA militant who was sentenced to death under the government of Francisco Franco and later was annnestied, recently has styled himself as a political leader willing to work within the political system.

Talking to reporters after receiving news of the arrests of his colleagues, Onaindia said the police actions could "overfill the cup in the Basque country" and he warned that a return to the "armed struggle" was on his group's agenda. A year ago the decision by the Basque Left to work within the system was hailed as evidence of the chances of stability.