Two years ago this week ETA's sudden announcement of an "indefinite" ceasefire raised widespread hopes in Spain that the long conflict in the Basque country was drawing to a close. No such optimism was sparked by the arrests of more than 30 ETA suspects last week, notwithstanding a rash statement by the Spanish Prime Minister, Mr Jose Maria Aznar, that ETA would be defeated "before too long".
There is, of course, a sense of relief that, after ETA's bloodiest summer campaign in many years, some major figures have been arrested. But there is also a weary feeling that things have merely returned to normal, in a pathologically abnormal situation.
Even that may be an optimistic analysis: a society can survive prolonged terrorist violence, but the polarisation in the Basque country between nationalists and non-nationalists is creating almost unbearable social tensions. In the words of a leading article in El Pais, Spain's sober newspaper of record, the Basque community now stands "on the brink of the abyss".
Last Friday evening, there were two demonstrations in San Sebastian. One was protesting against the arrests of ETA suspects, and had legal permission. The other was a spontaneous (and unauthorised) expression of anger at the shooting by ETA of a retired Socialist Party politician the previous evening. Jose Ramon Recalde, who is recovering in hospital, is a well loved and respected figure. Like several of ETA's recent targets, he played a significant role in the anti-Franco movement.
As the two hostile groups approached each other, they were separated by the Ertzaintza, the police force responsible to the Basque autonomous government. This government is controlled by moderate Basque nationalists. To the fury of many Spanish democrats, the Basque police followed the letter of the law, forcibly removing the anti-ETA protesters from the path of the ETA supporters. Only when the shouts of "ETA, kill them" from the latter group became deafening, did the police move against them also.
The approach by police epitomises the ambiguity towards ETA's violence for which democratic Basque nationalists are castigated by most other democrats in Spain. On the one hand, the moderate nationalists condemn every terrorist action by ETA. But they always add the violence cannot be ended by police methods alone. They argue that its root cause is a substantial political conflict over the right of the Basques to self-determination, which requires negotiation with ETA.
Mr Aznar's government, however, and the Socialist Party opposition, insist that since the Basques already enjoy extensive autonomy, and all normal democratic freedoms, there is no legitimate reason to negotiate with terrorists.
Meanwhile, daily life in the Basque country is corroded by mutual mistrust. It springs not only from fear of being included in ETA's ever-widening list of "legitimate" targets. The main factor is the kale borroka, an implacable campaign of street violence and vandalism waged by ETA's youth wing.
The main response to both threats from Madrid's centre-right government is a tough security policy, but without using the dirty-war methods which so tarnished its Socialist Party predecessors. Mr Aznar's administration is also planning anti-terrorist legislation, which has aroused concern among constitutional lawyers.
Will the strategy work, where it has failed so often in the past? Even as he enjoyed the success of last week's spectacular operations against ETA suspects, however, the Interior Minister, Mr Jaime Mayor Oreja, warned that the organisation would rebuild itself, as it has so many times over the last 40 years.
In the short term, the French and Spanish security forces seriously damaged several layers of what Basque radicals call the "national liberation movement" in last week's police operations.
Last Wednesday, the high-profile investigating magistrate, Mr Baltasar Garzon, the man who indicted Gen Pinochet, supervised Operation Black Wolf. Twenty middle-ranking members of ETA's political wing, Herri Batasuna, were arrested, and their offices were raided in three Basque cities.
On Friday, French police arrested a man described as ETA's "number one leader" in the French Basque town of Bidart. Ignacio Gracia Arregui is certainly a major figure in the movement. He is widely credited with restructuring ETA in the 1990s, after an earlier group of top commanders were arrested - also in Bidart. It is doubtful, however, that he is now as senior a commander as the police are saying.
His arrest was followed by the detention of more than a dozen other suspects in the French Basque country, the traditional base for ETA's leadership, over the weekend.
ETA has suffered a serious setback, after a few months when it often seemed able to operate with impunity.
The issue, though, is not the terrorist capacity of ETA but the militancy of its many followers in the Basque country. Allied to the ambiguous relationship which democratic nationalists continue to maintain with them, and the flat refusal of Madrid to countenance Basque "sovereignty", it threatens greater civil unrest.
Herri Batasuna has consistently enjoyed the support of about 15 per cent of the Basque electorate over the last 20 years. More moderate nationalists, like the Basque Nationalist Party, account for about 40 per cent more of the vote now, giving nationalists a narrow majority over non-nationalists.
The key to ETA's 1998 ceasefire was the Lizarra Pact, which committed all nationalist groupings to some form of Basque self-determination, beyond the limits of the current Spanish constitution. ETA returned to violence last December, accusing the moderates of failing to pursue this aim with sufficient vigour.
Since then, the moderate nationalists, who form a minority coalition in the Basque regional parliament, have severed political links with Herri Batasuna, but refuse to abandon the demand for self-determination. They insist ETA's supporters can only be won over from terrorism if this demand is at least put on the table.
This angers the centre-right Partido Popular government in Madrid, the opposition Socialists and most Spanish democrats. ETA's choice of left-wing victims over the summer appears to have been aimed at further poisoning this festering sore between nationalists and non-nationalists.
A sense of impotence among democratic anti-ETA sectors of the population is turning to combustible anger. They speak of "mobilising", not so much against ETA, but against ETA supporters. Such anger, while entirely understandable in the climate of terror which ETA has engendered, could feed the very conflict that is necessary to ETA's own survival. Twenty-five years after Gen Franco's death, the Basque conundrum looks as insoluble as ever.