By Mateus Maia and Jamie McGeever

BRASILIA, Feb 14 (Reuters) - Brazil President Jair Bolsonaro's government on Thursday released the first details of its long-awaited pension reform proposal, cheering investors who want to see the passing of legislation seen as key to shoring up creaky public finances.

Rogerio Marinho, secretary of social security and labor at the economy ministry, told reporters the government's bill will call for a minimum retirement age of 65 years for men and 62 years for women, and will be put to Congress on Feb. 20.

The transition period for these changes to be fully implemented will be 12 years, he added, after leaving a meeting with Bolsonaro and other cabinet members.

"The president has decided and asked us to divulge only some information, but the content of the text will be ready for Feb. 20," said Marinho. "The text is ready, it is already circulating in the internal organs of the government, and is just waiting to be validated with regard to its constitutionality."

The market reacted with delight at the government's plans, providing a rare bolt of good news for a young, ideologically disparate administration that has become snared in petty infighting and graft scandals in recent weeks.

Brazil's Bovespa stock market rose 2.05 percent, its best day since Jan. 2, while the real rallied further in unofficial after-hours trading.

Economy Minister Paulo Guedes said last month that total savings could reach 1.3 trillion reais over the next 10 years, and last week he said the aim was to save at least 1 trillion reais in a decade.

Many analysts are skeptical, arguing that savings may ultimately be less than half that 1 trillion reais figure because the government will be forced to water down proposals in order to get them through Congress.

It's not clear how much the official proposals to be put forward next week will save, but the market reaction suggested traders were happy.

"Finally, something official and reasonably clear," said Jose Francisco de Lima, chief economist at Banco Fator. "This will reduce uncertainty in a good way. Markets will like it."

Brazil's social security deficit was by far the biggest contributor to the government's overall fiscal shortfall last year, which widened 7 percent to 195.2 billion reais. In nominal terms, the pensions deficit has nearly quadrupled in four years.

To control those runaway costs, most analysts agree the government will have to make unpopular policy changes.

($1 = 3.7662 reais) (Reporting by Mateus Maia, additional reporting by Marcela Ayres, writing by Jamie McGeever and Gabriel Stargardter Editing by Susan Thomas)