MADRID (Reuters) - Public opinion in Spain has turned against King Juan Carlos in favor of his son Felipe, an opinion poll showed on Sunday, showing the toll taken on the king by gaffes, friendships with young women and royal family corruption allegations.

The survey for El Pais newspaper showed 53 percent disapproved of the 75-year-old king, giving him an overall approval-versus-disapproval rating of -11, compared to +21 in December. Prince Felipe's rating also fell but remained broadly favorable at +28, compared to +37 in December.

Juan Carlos's jet-set lifestyle and close friendships with young women, as well as a corruption investigation centered on his son-in-law Inaki Urdangarin, have left weary Spaniards sick of their royal family.

The poll was carried out before Princess Cristina, Urdangarin's wife, was charged last Wednesday with helping her husband in crimes that include fraud, tax evasion and embezzling 6 million euros of public funds from a charity.

By contrast, Felipe, 45, has not been touched by any of the royal family's scandals, and has benefited from an image as an active promoter of Spain. A poll in January found 45 percent of Spaniards wanted the king to hand over to him.

The king led the country's transition to democracy in the 1970s and won huge popular support after defusing an attempted coup in the 1981, but has increasingly appeared out of touch in a country with 26 percent unemployment.

His image was hurt when it was discovered he had been elephant hunting in Botswana last April while Spain looked close to requesting international financial aid.

The Metroscopia poll, which asked 2,400 people how they rated certain institutions, was carried out last month.

"We can see from the Metroscopia poll that the king has particularly lost support among socialist voters and young people," El Pais said. Those aged 18 to 34 gave the king a rating of -41.

The poll also showed general dissatisfaction with political institutions, with only 19 percent of those surveyed approving of the government and 93 percent disapproving of politicians.

If a general election was called now, the ruling center-right People's Party would receive just 24.5 percent of the vote compared to the 44.6 percent they received in the November 2011 election, while their socialist rivals would take 23 percent, a separate poll carried also published in El Pais showed.

(Reporting by Clare Kane; Editing by Peter Graff)