* Approval by parliament uncertain
* PM says vote will be a test of confidence
* Main rightist party backs plan, but accepts no changes
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(Adds main rightist party, background, market reaction)
By Jana Mlcochova
PRAGUE, Sept 21 (Reuters) - The Czech cabinet proposed tax hikes and spending cuts on Monday aimed at slashing the budget deficit and setting up a showdown with political parties, and it warned it may quit if the plan fails in parliament.
The Czech Republic has suffered a deep economic drop from record growth rates in the past years, exposing long-term erosion of the public budgets due to rising spending on pensions and welfare.
But politicians have been reluctant to commit to unpopular measures ahead of an election planned by mid-2010, leaving the interim non-political cabinet in a difficult position as it tries to put together next year's budget.
Prime Minister Jan Fischer told reporters the proposed measures would cut the central European country's 2010 fiscal gap to 5.2 percent of gross domestic product from 7.5 percent forecast under current legislation.
The package will go to parliament on Thursday and its fate is unclear mainly due to demands from the leftist Social Democrats to hike pensions and remove savings on welfare.
Fischer said the package would be a test of confidence in his cabinet, reiterating earlier hints that he may quit if parliament rejects it.
"I consider it possible to find a political agreement on the proposed package, however difficult it will be," Fischer said.
"Of course the result of the debate in the lower house will be a test of confidence toward the continuation of this government and depending on the result ... the cabinet and I personally will decide how to continue or not to continue."
The prime minister declined to directly say if he would resign in case the plan falls through, saying "resignations are to be handed in, not to be threatened".
Fischer said the measures would cut the central state budget gap, the main part of the overall public sector finances, to 155.3 billion crowns, compared with around 230 billion achievable without the changes.
PACKAGE PITS RIGHT AGAINST LEFT
The main rightist party, the Civic Democrats (ODS), grudgingly supported the package as a whole but would not accept any changes to it or approving it in parts.
"Calling this package a savings one requires a big dose of imagination," a vice-chairman of ODS, Petr Necas, said, citing its high proportion of tax hikes -- 50.3 billion versus 25.4 billion in spending cuts.
Necas said his party would support the measures but only if the leftist Social Democrats do not strip off any of the spending cuts during debate in parliament.
That is exactly what the Social Democrats plan to do. They had no immediate comment on Monday but have said in the past days that any savings on welfare were unacceptable, and on top demanded a hike in pensions.
Finance Minister Eduard Janota said the package would have a negative impact on GDP of around 0.6 percent, bringing growth next year to about -0.3 percent.
Fischer's cabinet was due to leave after an early election in October, but the plan to hold the polls failed due to a court ruling and a withdrawal of support for early election by the Social Democrats. The regular term ends in June next year.
The crown extended earlier losses after the news, giving up gains with other central European currencies to bid down 0.2 percent on the day at 25.154 to the euro. (Writing by Jan Lopatka; Editing by Stephen Nisbet)