DUBLIN - Irish opposition leaders vowed Thursday to rewrite the country's harsh four-year austerity plan if they oust Prime Minister Brian Cowen's government in early elections next year.

Cowen unveiled a package of tax increases and spending cuts Wednesday aimed at reducing Ireland's massive budget deficit, necessary to receive a euro85 billion (US$115 billion) bailout from the European Union and the International Monetary Fund.

The plan seeks to cut euro10 billion (US$13.3 billion) from spending and raise euro5 billion (US$6.7 billion) in extra taxes from 2011 to 2014. Cowen himself has acknowledged the measures would lower the living standards of everyone in Ireland.

Cowen faced more pressure Thursday as voters in northwest Ireland were expected to snub his Fianna Fail party's candidate in a byelection -- making it harder for him to pass the emergency 2011 budget. The vote in Donegal South West fills a parliament seat that Cowen left empty for 17 months in fear that an opposition candidate would win.

Enda Kenny, leader of the main opposition Fine Gael, told Dail Eireann, Ireland's parliament, that his party would redraft the plan if it wins power.

"The next government will not be bound by it," he said.

Cowen has said a national election will be called when Ireland's emergency 2011 budget, to be unveiled in parliament on Dec. 7, is fully enacted. His party is then expected to be ousted from office.

Labour leader Eamon Gilmore said the deficit plan had too little details on how to create new jobs and few new ideas.

"This plan is the price of political failure, and it's very heavy price indeed," Gilmore said.

Finance Minister Brian Lenihan says the austerity plan is the only realistic approach to Ireland's staggering financial problems, brought on by reckless bank lending for overpriced real estate.

"How arrogant can you be? This from a minister who presided over the greatest economic catastrophe in this nation's history," Kenny told lawmakers.

Pearse Doherty of the Irish nationalist Sinn Fein party -- the favorite in Donegal South West -- is committed to voting against the budget. The result will be announced Friday.

An opposition win would reduce Cowen's parliamentary majority to two.