Sinn Féin is confident of winning 14 seats in the next general election and may want to take part in a coalition, the party's Cavan-Monaghan TD Caoimhghín Ó Caoláin said.
"We have ambitions that can only be achieved in power. I think Sinn Féin is able and has already demonstrated its capacity for responsible government," he said.
He sharply criticised Fine Gael and Labour for opposing plans put forward by Taoiseach Bertie Ahern to let Northern MPs, including those of Sinn Féin, address Dáil Éireann.
Naming Sinn Féin's target gains, Mr Ó Caoláin identified Cork North Central, Donegal North East, Donegal South West, Waterford, Wexford and two extra but unnamed Dublin constituencies.
Sinn Féin, he said, will decide on its attitude to coalition at a special ardfheis after the election: "The electorate's decision will decide our future actions," he said.
Questioned on a nearly complete review of the party's economic policies, which recommends a 50 per cent tax band for those earning more than €100,000 a year, he said the party had no desire to raise taxes for the sake of it.
The review, chaired by party chairman Mitchel McLaughlin, also favours increasing corporation tax to 17.5 per cent and giving councillors control over stamp duty rates.
Sinn Féin would prefer if improvements could be made to public services, especially the health service, through reform and efficiencies rather than through extra spending, he said.
"However, we are not opposed to increasing taxation at any cost. We have to be open and honest. We have been prepared to say that we would be prepared to do so, if necessary," Mr Ó Caoláin said.
Many voters, he said, would be prepared to pay extra tax if it meant they did not have to pay for private health insurance to guarantee "themselves a decent level of care. This is not something that we have been saying on our own. The Irish Congress of Trades Unions has been saying exactly the same thing. But we are the only political party prepared to say it."
Following the next election, Sinn Féin would "actively consider" coalition, even though many in the party were "not wild about the idea".
"Make no mistake about it, however, this is a nettle that Sinn Féin will grasp. The only question is when. The only party that we would absolutely rule out are the Progressive Democrats."
The review of the party's economic policies, led by Mr McLaughlin and former general secretary Robbie Smyth, has been under way for over a year.
Stamp duty revenue on new and second-hand house sales would be split between central and local government, rather than going entirely to the Exchequer - though councillors would set the rate in their own local areas.
Meanwhile, Sinn Féin has urged the Taoiseach to push ahead with plans to let Northern MPs speak on Northern Ireland-related issues and the Belfast Agreement in the Dáil.
Mr Ahern has proposed that the full Dáil of 166 TDs should meet as a committee of the House to hear such speeches, though Fine Gael and Labour believe it would merely award a major propaganda victory to Sinn Féin.
In a letter yesterday to the Taoiseach, Mr Ó Caoláin said he had understood that Mr Ahern's original letter had been written "in the terms of a decision rather than a proposal". He said he understood the Taoiseach was seeking agreement from the other parties "on the format and agenda of the meetings", rather than on the principle itself.
