WARSAW (Reuters) - Polish Prime Minister Donald Tusk said on Wednesday he was promoting his finance minister, Jacek Rostowski, to the post of deputy prime minister.

He said Rostowski would keep his job as finance minister after the promotion.

"The finance minister should have a stronger position," Tusk told a news conference. "Poland's growth and public finances, our fiscal discipline, will be the government's priority."

Markets credit Rostowski with overseeing Poland's fiscal discipline and careful stewardship of the economy. Until a slowdown hit last year, those policies helped sustain growth in Poland even as its neighbors were in recession.

Rostowski has said he is determined to reduce the country's deficit, now expected to drop to about 3.4 percent of gross domestic product (GDP) in 2012. European Union rules set the deficit ceiling at 3 percent of GDP.

The finance minister, 61, was born in London into a family of Polish exiles. He spent part of his childhood in Africa where his father, who worked for the British diplomatic service, was posted. He was appointed finance minister in 2007.

Tusk also said on Wednesday there would be a bigger government reshuffle half way through this year.

(Reporting by Dagmara Leszkowicz; Writing by Karolina Slowikowska; Editing by Christian Lowe, Ron Askew)