* Immigration Minister Scott Morrison promoted to Social Services portfolio
* Gaffe-prone Defence Minister David Johnston out
* New Health Minister Sussan Ley becomes second woman in cabinet (Updates with detail)
By Jane Wardell
SYDNEY, Dec 21 (Reuters) - Australian Prime Minister Tony Abbott, battling a slide in public support, reshuffled his cabinet on Sunday, promoting the overseer of a tough immigration programme and throwing out his gaffe-prone defence minister.
Abbott said the shake-up was for jobs and families and stressed a focus on financial issues as he deals with the fallout of an unpopular belt-tightening budget.
"It is a sign that this government wants the economy to be front and centre in the coming year," he told reporters in Canberra.
Abbott is nearing the end of his first full year in office hobbled by missteps and a souring economy that have dragged his approval ratings to historic lows.
Faced with a collapse in commodity prices and an unruly upper house Senate, that has held Abbott's first budget hostage since May, voters have abandoned his conservative government more quickly than any other in three decades.
The elevation of Immigration Minister Scott Morrison to social services minister underscored the shift in priorities away from the secretive programme of "turning back the boats" of thousands of asylum seekers that helped it win power a year ago.
That policy has been criticised by the United Nations, but Abbott lauded Morrison as "the master of difficult policy and administration" for almost entirely stemming the flow of boats over the past year.
"He is a very tough and competent political operator," Abbott said of Morrison. "He's also a very decent human being."
Defence Minister David Johnston lost his job in the reshuffle which came a month after he embarrassed the government with comments critical of government-owned ship-builder ASC, saying he did not trust it to "build a canoe".
The comment fuelled expectations that most of the work in an A$40 billion submarine programme will go offshore.
Reuters reported in September that Australia was leaning toward buying up to 12 off-the-shelf stealth submarines from Japan.
Morrison will be replaced by Peter Dutton, a former police detective, in the new portfolio as Minister for Immigration and Border Protection. Johnston will be replaced by Kevin Andrews.
Abbott also appointed a second woman to his cabinet, following criticism of a lack of female representation. Sussan Ley was promoted to minister for health and minister for sport, joining Foreign Minister Julie Bishop.
"All of our appointments are on merit," Abbott said when asked if two women was enough. "As time goes by and the number of women in the parliament increases, I'm confident that there will be more." (Additional reporting by Morag MacKinnon in PERTH; Editing by Robert Birsel)