(Adds delays at Belo Horizonte, comments from Pele and minister)
By Brad Haynes and Anthony Boadle
SAO PAULO/BRASILIA, April 7 (Reuters) - With less than 10 weeks until the start of the World Cup, work on crucial new airport terminals has fallen behind in most of the dozen Brazilian host cities, heightening the risk of overcrowding and confusion during the tournament.
A temporary canvas terminal will be used instead of a planned airport expansion to receive fans in Fortaleza, which will host six matches including Brazil's game against Mexico.
During President Dilma Rousseff's visit to an airport in Belo Horizonte, the site of a semi-final, officials admitted on Monday that construction would not be completed in time.
Back-up plans are also being prepared in other cities.
"Other airports have not said anything yet, but they will probably have to come up with contingencies," said Carlos Ozores, a principal at aviation consultancy ICF International who has consulted for Brazilian airlines and airport operators.
Concern over Brazil's airports is especially acute since they represent some of the tournament's most lasting investments. A host of other transportation projects have been scrapped or postponed, adding to criticism that the World Cup will leave few long-term benefits for ordinary Brazilians.
Soccer legend Pele said on Monday he worried that the state of Brazil's airports could ruin the opportunity presented by the tournament, adding that he was saddened to see rushed efforts when his country had years to prepare.
Quick fixes and last-minute deliveries are a recipe for chaos in the complex aviation industry, analysts say. Bungled openings of terminals from London to Denver took months to straighten out.
The stakes will be high in Brazil as more than 600,000 visitors arrive for the World Cup starting in June, one of the biggest sudden influxes the country has ever seen.
"People coming to Brazil are going to be shocked, especially Americans, by the how bad the airports are," said Paul Irvine, who runs travel agency Dehouche in Rio de Janeiro.
"There won't be any catastrophic issues ... but they will be chaotic and ugly as heck," he said.
Any air travel chaos could be especially embarrassing for President Dilma Rousseff, who made a bold political bet by privatizing a handful of key airports to ready them for the tournament, accelerating work that had languished under state control. The move broke with the ideology of her leftist Workers' Party.
If those airports fail to deliver the smooth service that helped to justify the privatizations, the issue could quickly become an election campaign issue as Rousseff seeks a second term in October. The airport concessions are a closely watched first step in her more than $100 billion plan to draw private investment to public infrastructure projects.
Construction delays at publicly administered airports have been far more dramatic. At the start of last month, airport overhauls in seven World Cup host cities were only half finished or worse, according to Infraero, the government agency that oversees airport operations.
Brazil's civil aviation minister, Moreira Franco, said the airports can handle World Cup crowds despite the delays, and ongoing construction will be covered up during the tournament.
"Unfortunately, Infraero makes a real mess of an airport when it is doing work. Infraero and the operators will not be allowed to turn travelers' lives upside down," he told Reuters on Monday.
The privately run projects are also drawing scrutiny. Civil aviation authority ANAC has redoubled its inspections of three privatized airports since learning at the start of this year that work was behind proposed timelines.
At the international airport serving the capital Brasilia, the racket of jackhammers rings through an open concourse, where passengers riding up an escalator can see a six-foot wide hole in the floor behind a boarded-off area.
One new terminal is set to open in weeks and the private operator promises another by May, although municipal authorities are downplaying that possibility.
At Guarulhos Airport outside of Sao Paulo, Brazil's biggest city, the glistening facade of the new Terminal 3 hides an interior still missing several walls, ceilings and basic operating systems.
"Guarulhos is where we expect to get the most blowback," said one government official briefed on the airport's progress, who requested anonymity given the sensitivity of the issue.
The automated baggage check and immigrations systems originally promised will not be ready for the World Cup. The new international terminal is set to open at a fraction of its eventual capacity, handling just one in four foreign flights - less than 10 percent of overall traffic at the airport.
"At Terminal 3 in Guarulhos, they have already shifted from more airlines to fewer for the World Cup, and one could imagine further announcements ahead," said Ozores. "There's clearly a correction going on, an adjustment of expectations."
By most accounts, construction at the privatized airports has moved at a relentless pace, with as many as 8,000 workers on shifts around the clock at each site. Operators say they will deliver new terminals by the deadlines they promised.
But the timelines for the airports were tight from the start. After winning auctions in February 2012, paperwork and regulations held up construction until the second half of the year, leaving airports with as little as a year and a half for their overhauls.
Viracopos, another privatized airport outside of Sao Paulo where several national teams will be chartering flights, was 82 percent finished with its promised expansion in January, about three months before its deadline. Its operator declined a request to visit the site.
By contrast, several World Cup stadiums were finished late, but organizers have now held test matches in all except one of 12 scheduled to host games: Sao Paulo's Arena Corinthians, where the deaths of three construction workers have slowed work amid investigations.
Brazil's need for new airport terminals is unmistakable, with three in four airports stretched beyond intended capacity since 2010 after air traffic more than doubled in a decade, according to Infraero.
However, the scramble to finish construction on the eve of the World Cup has created the potential for snags in a system with little margin for error.
The Brazilian Air Force has further complicated things by declaring no-fly zones over stadiums during matches for security reasons, disrupting flights in several cities for as much as five hours at a time.
Brazilian airlines have also been cutting costs and slashing payrolls after two years of heavy losses, and travel headaches are common in the country even without the crush of a major sporting event. During a recent visit to the Brasilia airport, for example, one airline's computer system crashed for hours, sending queues snaking out the door and along the curb.
"It will be chaotic and strange situation for most travelers," said travel agent Irvine of Dehouche. "But they will muddle through." (Additional reporting by Leonardo Goy; Editing by Kieran Murray)