* Parliament expected to vote on Wednesday
* Four parties to support PM candidate (Adds move for no-confidence vote, date of session)
By Marja Novak
LJUBLJANA, Feb 22 (Reuters) - Slovenia's main opposition party on Friday moved to hold a "constructive no-confidence vote" next week to replace conservative leader Janez Jansa, whose majority in parliament is dwindling as parties drop out of his coalition.
The centre-left Positive Slovenia (PS), which earlier named its candidate for prime minister, financial expert Alenka Bratusek, filed a motion to hold the vote at an extraordinary parliament session on Wednesday.
Such a vote would allow parliament to oust the prime minister and approve a successor in a single vote. Bratusek is virtually certain to be endorsed as the PS has already secured the support of other opposition parties.
Jansa, whose reputation has been damaged by a corruption scandal, lost a second member of his ruling coalition on Friday when pensioners' party Desus formally quit. He is expected to lose a third party on Monday.
The defections will leave him with only 30 out of 90 seats in parliament, unable to govern effectively but still clinging to power.
The opposition parties agreed that Bratusek would call for a confidence vote after one year in office, which would allow parliament to oust her, triggering a snap election. A regular ballot is due in late 2015.
"There is a good chance that Bratusek will be voted in because the parties simply want to get rid of Jansa," Meta Roglic, a political analyst of daily Dnevnik, told Reuters.
Earlier on Friday Desus, the centre-left Social Democrats and the centre-right Civic List confirmed they would give their support to Bratusek after PS leader Zoran Jankovic, also implicated in a corruption scandal, said he would resign as head of the party once Bratusek's government is approved.
The four parties have 49 out of 90 seats in parliament and need 46 to win the vote.
If elected, Bratusek, 42, who oversaw the state budget at the finance ministry for six years before entering parliament in December 2011, will become Slovenia's first female premier.
She will then have up to 15 days to propose her cabinet, which also needs to be confirmed by majority of parliament.
The new government will have to reform the banking system, which is struggling with a rising amount of bad loans, increase labour flexibility in the country, sell some state firms and possibly increase the value added tax to reduce the budget gap.
Export-oriented Slovenia was badly hit by the global crisis and fell into a new recession last year due to lower export demand and a fall in domestic spending caused by budget cuts.
It hopes to reduce the budget deficit to 3 percent of GDP this year from 4.2 percent in 2012.
European Economic and Monetary Affairs Commissioner Olli Rehn said earlier on Friday Slovenia would not be able to meet its 2013 deficit target because of its ailing banking sector, burdened by 7 billion euros of bad loans, which is likely to need a financial lifeline from the state.
In October the government managed to issue its first sovereign bond in 19 months, avoiding having to go to its European Union partners for a bailout at least until June.
"This (nominating a new prime minister) is a step forward towards avoiding a bailout but the new government will soon have to take further steps to overcome it," Roglic said. (Editing by Zoran Radosavljevic and Sonya Hepinstall)