One year later, Europe’s fight against terrorism remains hampered by some of the same national rivalries, fragmented intelligence services and bureaucratic obstacles that existed before the blasts of March 11, 2004, according to analysts, diplomats and other experts. About 75 people — the majority of them Moroccan nationals — have been arrested in connection with the attacks, and 23 remain in prison. But central questions of who organized them, and how, remain unanswered.

Shortly after the bombings, the European Union created the post of counterterrorism coordinator to facilitate cooperation among European governments. It appointed a Dutchman, Gijs de Vries, to the post, but the position lacks real power or resources, and intelligence officials in E.U. countries continue to resist sharing their most sensitive data.

Many proposals raised just after the attacks — for a Europe-wide fingerprint and DNA database and biometric passports, for instance — remain just proposals. Plans for a common arrest warrant, to make extradition of suspects easier, have faltered because some countries have withheld approval.

Despite five decades of economic and political integration in Europe, national governments retain major powers and often undermine standardization plans that originate in Brussels, headquarters of the 25-nation European Union. Even when political will exists, the E.U.’s tangle of rules and regulations can stall change for years.

“We are on the right way, but we didn’t go far enough,” said Berndt Georg Thamm, a terrorism expert in Germany who works with the country’s security agencies and military. “The big bang of 11 March pushed the European Union in the right direction,” he said, but added that it would “take some years before we have complete international, and also national, information-centered cooperation.”

“There’s a lot on paper,” said Daniel Keohane, a researcher with the London-based Centre for European Reform. “They have an action plan with over 100 measures . . . the whole gambit of cooperation. But the E.U. is not a government. It doesn’t have its own intelligence resources.”

“Britain, France, Germany, Italy and Spain, which have the greatest intelligence resources, don’t want to share with the 25,” he added.

Another subject awaiting more action is control of financing. “Terrorists have found new ways to finance their activities, resorting to petty crime and fundraising within their communities, which is much more difficult to trace,” said Loretta Napoleoni, author of the book “Terror Inc.: Tracing the Money Behind Global Terrorism.”

Napoleoni was in Madrid attending the International Summit on Democracy, Terrorism and Security, an annual event scheduled for March this year to commemorate the attacks. She coordinated a work group on terrorism financing, which recommended that the United Nations set up a finance monitoring center to help with intelligence and intergovernmental cooperation.

Even here in Spain, scene of the attacks, many of the pre-March 11 problems persist. In the weeks following the train blasts, Spaniards pledged to find ways to increase security and prevent attacks. But other than increasing communications channels among the security and intelligence branches and adding Arabic-speaking intelligence and judiciary workers, not much has been accomplished, according to security experts.

Immediately after the attacks, many European countries stepped up security at crowded rail stations. For a while, there was talk of setting up airport-style security systems at stations, but the idea was soon abandoned.

At commuter train stations across Madrid, there are no visible signs of heightened security a year after the attacks. “We have increased security in every possible way,” said Joaquin Ruano, who heads the security division of the rail company Renfe. “But there is an average of 885,000 travelers per weekday in Madrid alone. It’s very hard to control that.”

“People think about it as they get on the trains, and there is still fear,” said Cristina Cobo, a daily commuter at Madrid’s Atocha station, the destination of the bombed trains.

A year after the attacks, some key details of the plot remain largely unknown. Much about the culprits and their exact motives is still a mystery, and large parts of the investigation, conducted by the Spanish judiciary, are under a news blackout.

The government attributes the attacks to Islamic radicals linked to al Qaeda. The Popular Party — in power at the time of the attacks — stands by its initial suggestions that the Basque separatist group ETA was involved. The national daily El Mundo, which has broken several stories on the investigation, has reported extensively on an alleged connection involving elements of the Moroccan secret security services. The Moroccan government denies the allegation.