The Green Party has lost its legal challenge against a decision by RTÉ which resulted in its exclusion from the political parties' leaders' debate which takes place tonight.

Ms Justice Marie Baker said the criteria used by RTÉ was not unfair or irrational or disproportionate.

The Green Party was not invited to participate in the leaders' debate because it has no sitting TDs in the outgoing Dáil.

In a two-day hearing at the High Court last week the party argued that the RTÉ requirement to have at least three TDs was unfair, unlawful and an interference with democracy.

It complained that some of those who will take part in the debate belong to parties that did not even exist before the last general election and their representation in the Dáil was a measure of support for their former parties and policies rather than their present positions.

The Greens had argued that "as a former partner in Government and an established presence" on the Irish and international political scene, it should not be excluded from the debate.

Its lawyers argued the decision was a breach of constitutional rights and the Broadcasting Act.

RTÉ denied the claims and said the leaders' debate was just one of many programmes covering the General Election.

It said the method for deciding participation in the debate was fair, impartial and objective and was put in place following an extensive review by a steering committee.

The broadcaster said it applied the criteria equally to all political parties in the State.

The station did not accept that the exclusion of Eamon Ryan would skew voter choice pointing to the last leaders' debate in which the Green Party took part but failed to win any seats whereas others excluded from the 2011 debate went on to win six seats.

Ms Justice Baker said RTÉ accepted that the editorial criteria that it has adopted for the election were not perfect.

She said she accepted the general proposition that some threshold requirements and some editorial choice to enable the production of an attractive and engaging programme had to be made.

She said she did not consider the criteria were unfair or irrational.

"I also do not consider them to be disproportionate to the aim to be achieved in particular I consider the interest of the viewer in an attractive and engaging programme, the importance of current Dáil representation as an index of political thinking and the spectrum of opinions all have to be weighed in the balance," she said.

"I cannot also omit to take account of the extent to which the role of RTÉ as an expert must be respected by the court and which is given its singular recognition in the Constitution.

"It is not merely that the court cannot produce a television programme but the court cannot be asked to fix programming criteria in which it has no expertise," she said.

The judge added: "I consider that RTÉ is amenable to review in the choice of criteria and that fundamental and core democratic ideals are in play in the present case.

"I consider that the criteria adopted for participation in the debates are sufficiently reasonable and impartial and that they are proportionate to the needs of the political debate and the right of the public to be informed and educated in an engaging live programme."

The issue of costs has been postponed until later this month.

Mr Ryan said he was obviously disappointed with the judgment but appreciated how both sides conducted the case.

He said the case was "very worthwhile and very useful".

He said he was disappointed that he would not be travelling to Limerick tonight but would like to see the Greens playing a central role in the remainder of the campaign.

Mr Ryan said the case raised important democratic and judicial issues to be considered and he welcomed the fact that the judge "recognised that key issues had to be worked through".

Speaking following the ruling, Green Party leader Eamon Ryan said: "We thank both legal teams for arguing the case in a respectful manner and appreciated the concluding comments of Judge Baker where she acknowledged that: 'RTÉ accepts that the editorial criteria that it has adopted for this election are not perfect, and it is not suggested that they would be suitable in another electoral context.' and that: 'fundamental and core democratic ideals are in play in the present case.'

"We are disappointed that despite such reservations she deemed that the criteria being used were sufficiently reasonable for the courts not to interfere in the matter.

"We will now redouble our efforts in the remaining days of the campaign to get our message heard," Mr Ryan added.