By Joan Faus

BARCELONA (Reuters) -Spain's Catalonia region on Tuesday approved a 3.2 billion-euro ($3.7 billion) expansion of Barcelona's airport, angering environmental groups and campaigners against excessive tourism.

The project, to be paid for by Spanish airport operator Aena, could be a test case for the European Union, which will have to decide whether to back the expansion near an environmentally protected area as it seeks to cut pollution.

It also flies in the face of Barcelona's stated plans to reduce visitor numbers amid growing anger from residents over the impact of mass tourism.

Catalonia's president, Salvador Illa, said expanding the airport was critical for it to become a major hub for intercontinental connections, offering more flights from Asia and the Americas to attract talent and investment as Spain strives to focus on a smaller number of wealthier tourists.

"I honestly believe that the project is technically the best and most balanced ... and I am satisfied with the ambition of the measures and the environmental trade-offs associated," Illa said at the regional government palace.

A Catalan government source told reporters that authorities were "totally convinced" the expansion would be given the green light by Brussels.

The plan would extend one of the airport's main runways by 500 metres, affecting 27 hectares of a wetland area protected by the EU's Natura 2000 programme. In exchange, about 250 hectares in the surrounding area would be turned into green areas.

Authorities plan to start construction by 2030 and for the expansion to be completed by 2033.

They plan to request approval from the European Commission by 2028 and to receive an answer the same year regarding the protected areas.

The deal between Spain's Transport Ministry, Catalonia's government and Aena also includes the construction of a satellite terminal. The expansion would increase the airport's capacity to 70 million passengers per year from 55 million.

Aina Vidal, a lawmaker from the national government's junior coalition partner Sumar, said Barcelona was already overflowing with tourists.

"More airplanes mean more pollution for a city that is already at its limit," Vidal told reporters.

Spain last year received a record 94 million tourists, making it the world's second-most popular destination after France.

($1 = 0.8757 euros)

(Reporting by Joan Faus, Inti Landauro and David Latona. Editing by Barbara Lewis, Charlie Devereux and Mark Potter)