MADRID (Reuters) - Staff at El Pais, one of Spain's most popular newspapers, went on strike on Tuesday over management plans to slash the workforce in a bid to prevent the publication becoming a casualty of the country's economic crisis.

Workers posted pictures of an empty newsroom on the web and said on Twitter that 95 percent of the newsroom staff were observing the strike, due to last three days.

A company spokeswoman said 79 percent of total staff had backed the strike.

"The strike has been a success, the newsroom is practically empty. There are only some subdirectors and managers there," a representative of the workers' committee said.

Dozens of publications and media outlets in Spain have closed since the country's economic crisis erupted in 2008 as a housing boom fueled by cheap credit turned to bust. Advertising revenues have plummeted.

El Pais was founded in 1976, during Spain's transition to democracy following the death of dictator Francisco Franco and gained a reputation as the newspaper of democratic Spain.

But it ran into debt troubles when it bought out the minority shares of its Sogecable pay-TV unit soon before the 2008 financial crisis.

Over the years, many well-known Spanish and Latin American novelists have contributed to the newspaper. Mario Vargas Llosa, the Peruvian author who won the 2010 Nobel Prize for Literature, was among a group of writers who wrote to the newspaper to express concern about lay-offs.

Workers had called off a previously planned strike as they negotiated with Spanish media group owner Prisa but discussions reached an impasse.

Management has offered to scale back planned dismissals to 139 out of the paper's 460 posts and cut salaries for remaining staff by 13 percent. Staff rejected this new proposal.

The management plan also includes early retirement for some workers. Staff took a pay cut of around 20 percent in 2011, the workers' representative said.

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Prisa lost 31 million euros between January and September this year. The company, with assets across Latin America and Europe, said strong growth overseas was overshadowed by weakness in print media and radio, particularly in Spain.

Prisa's Chief Executive Juan Luis Cebrian angered staff with comments two weeks ago that workers over 50 no longer fitted the newspaper's profile.

"We can't keep living so well," he said.

Cebrian earns 13 million euros a year and workers facing pay cuts have demanded he return some of his high salary.

Advertisers in Spain expect to spend 15.1 percent less this year, according to a survey published by media consultancy Zenith.

El Pais had an average circulation of 345,000 in the year to end-June 2012, according to Spain's circulation registry (OJD). The Madrid-based paper reported last Tuesday that it had made a loss for the first time this year.

El Pais has regional offices in Spain and is also printed across Latin America and in Britain, Italy and Belgium.

(Reporting by Robert Hetz; Writing by Clare Kane and Sarah Morris; Editing by Tracy Rucinski and Angus MacSwan)