In Catalonia, Spain, Artur Mas Is Separatist Voice Edu Bayer for the International Herald Tribune "Our ideal is to be part of the United States of Europe," said Artur Mas. BARCELONA, Spain - ARTUR MAS, the leader of Catalonia, has a clear message for Madrid: He is serious about his threat to let the people of Spain's most economically powerful region decide for themselves in a referendum whether they should remain a part of Spain. In fact, he said in an interview this week, he would personally vote for independence if the opportunity arose. "Our ideal is to be part of the United States of Europe," he said. That kind of posturing has thrust Mr. Mas, 56, to the forefront of Spanish politics and made Catalonia the biggest domestic headache for Prime Minister Mariano Rajoy, who is facing troubles on all sides as he tries to satisfy demands from the European Union to straighten out Spain's economy and from Spain's heavily indebted regions, including Catalonia. The question now for Mr. Rajoy, and for all of Spain, is just how far Mr. Mas, a once relatively obscure politician who was elected regional president two years ago, is willing to go in posing what may be the most serious challenge to a sovereign entity in Europe since the implosion of Yugoslavia in the 1990s. Mr. Mas's talk is not idle. With a $260 billion economy that is roughly the size of Portugal's, an independent Catalonia and its 7.5 million inhabitants - 16 percent of Spain's population - would rank ahead of a dozen of the 27 nations in the European Union. But like most of Spain's regions, it is under great financial pressure and would like a better deal from Madrid. In that respect, his threats may amount to nothing more than brinkmanship, as he applies to Madrid much the same tactic it has used to gain favorable treatment in its own dealings with Brussels: that is, that Catalonia, which has its own language and sense of identity, is simply "too big to fail" without calamitous consequences that no one wants to see. On Friday, Catalonia's government raised the pressure, saying it would not be able to meet its September payments for basic services like heath care on schedule. The great risk is that Mr. Rajoy's government - squeezed as it is, itself weighing a European bailout - is hardly in a position to appease Catalonia's demands under a Spanish tax system that redistributes revenue from the richest to the poorest regions, without also raising tensions with other struggling regions. The grievances run in both directions. In Catalonia's view, Madrid has drained its finances, while Madrid accuses Catalonia, like nearly all of Spain's regions, of mismanaging its books. In the interview on Wednesday in the Catalan government's medieval palace, Mr. Mas was unrepentant about further unnerving investors who already question Mr. Rajoy's ability to meet agreed deficit targets and clean up Spanish banks. Instead, he contended that it was Mr. Rajoy who had forced Catalonia down the separatist path, after rejecting its demands unconditionally. "When you get a clear no, you have to change direction," Mr. Mas said. Although he acknowledged that there was no guarantee Catalonia would succeed in imposing its claims on Madrid, he argued that "the worst-case scenario is not to try, and the second-worst is to try and not get there." HIS advice to Mr. Rajoy was to avoid further delay in tapping a bond-buying program, devised by the European Central Bank largely with Spain's rescue in mind. European financing - in the form of billions of dollars in subsidies received after Spain joined the European Union in 1986 - had already played a major part in Spain's development, he noted. "The problems of Spain now supersede its capacities, so that it needs help," Mr. Mas said. If you have no other choice than to ask for a rescue, the sooner the better. Asked, however, where Spain would stand without Catalonia, its industrial engine, Mr. Mas was unperturbed. "Spain without Catalonia is not insolvent but more limited," he said. An economist by training, Mr. Mas comes from a Catalan family linked to the metal and textile sectors, which were at the heart of the region's development after the Industrial Revolution. Having studied at a French school in Barcelona and then learned English, he also stands out as a rare multilingual leader in Spain's political landscape.