UPDATE 1-Bank of Portugal warns of bailout implementation risk

* 78-billion-euro EU/IMF bailout approved earlier this week

* Cenbank says implementation needs wide political support

* Portugal holds snap general election June 5

(Adds quotes, background)

LISBON, May 19 (Reuters) - The Bank of Portugal warned on Thursday that the country's economic programme under its EU/IMF bailout has significant implementation risks, making it essential that it receives wide-ranging political and social backing.

The central bank said in its annual report that the adjustment programme under the three-year, 78-billion-euro rescue package approved by euro zone finance ministers this week is balanced and could bring economic growth in the medium term.

"Still, there are significant implementation risks, which are both internal and external," it said. "At the internal level, it will be essential to ensure wide-ranging and stable social and political support, based on a common view of the medium- and long-term benefits."

The bailout package, requested by the caretaker government of Socialist Prime Minister Jose Socrates last month, received support from the main opposition Social Democrats and the rightist CDS-PP.

But Socrates' resignation in March means Portugal will hold a snap general election on June 5, with opinion polls showing the race is still open, although the Social Democrats have held a slight lead in most surveys. It will be up to the next government to enact the bailout programme.

The central bank added that wide support for the plan was key to "contain and reduce pressures from entrenched interests and to unblock institutional impasses".

Much of the pre-electoral debate has centred on the role and cost of public-private partnerships, as well as the weight of the public sector and state-owned companies on the economy.

The Bank of Portugal said wide political support would be key to meet the targets set out in the programme, which include cutting the budget deficit to 5.9 percent of gross domestic product this year from last year's 9.1 percent.

The Portuguese economy is expected to contract 2 percent this year and by the same level in 2012 due to the steep spending cuts and tax increases in the bailout programme.

"This prolonged recession will be accompanied by an unprecedented drop in families' disposable incomes and new increases in unemployment rates," it said. (Reporting by Shrikesh Laxmidas; Editing by Axel Bugge and Catherine Evans)