The Taoiseach has called for an overwhelming endorsement of the Belfast Agreement, saying it marked a "defining moment for Fianna Fail".
Opening what he promised would be a vigorous Fianna Fail campaign for a Yes vote on May 22nd, Mr Ahern criticised "intolerant . . . fundamentalist" opposition.
"If ever there was a case of an important civic duty it is on May 22nd, to give an overwhelming popular endorsement to the Good Friday Peace Agreement reached in Belfast."
He also condemned the "territorial mindset" of the British army which was responsible for an unacceptable level of activity in south Armagh.
Mr Ahern said his party would conduct a vigorous referendum campaign, publishing posters and literature. The Taoiseach and his Ministers would campaign throughout the State.
Appealing for a high turnout and a strong Yes vote, he said: "It is not so much the result itself but the strength of the result that will count . . . It is very important that there should be a high Yes vote, not just amongst those who vote but amongst the electorate as a whole.
"Let us show that we really care - that we do not want to see anyone else killed, any more families bereaved - by turning out to vote."
The referendum marked "a defining moment for Fianna Fail, that has been the standard-bearer of democratic republicanism in this jurisdiction for over 70 years".
People in the Republic had to be prepared to move and to accept constitutional changes. "Without our willingness to contemplate balanced constitutional change as part of an overall agreement, there would have been no negotiations, no agreement and, in all probability, there would be no peace."
He said that in the future neither tradition and neither government could unilaterally lay down the law. The proposed changes in Articles 2 and 3 would bring the immense psychological gain of "defining our nation in generous and inclusive 32-county terms and by putting people before territory".
The proposed amendments of the Constitution were "part of removing the strong mutual antagonism from political life on this island, and replacing it by more co-operation and working together, as well as creating more room and respect for difference".
He criticised "intolerant . . . fundamentalist" opposition to the agreement. On the one hand, there were "those who want to ignore the Irishness of the nationalist community completely and deny them any communal rights or political identity by simply integrating Northern Ireland into Britain".
On the other side were "certain republican fundamentalists who basically want to maintain the right or the option to carry on the armed struggle. They cite in their justification a declaration that is 80 years old that provides no answers to the problems of the North that that period conspicuously failed to solve".
These people invoked "the memory of the best known of the hunger-strikers [Bobby Sands]".
"But no one can presume that he would have been opposed to the peace initiatives of his fellow leaders in the republican movement. Fundamentalism is sterile, and leads nowhere except to more pointless grief. It has no significant support among Irish people at home or abroad."
Mr Ahern criticised the British security forces' behaviour in south Armagh, saying the British army appeared not to have given up its "territorial mindset" despite the ceasefires.
"It is unfortunate that the people of south Armagh, nearly 12 months into a ceasefire, should still be treated as if they were living in occupied territory . . . The landscape of south Armagh has a frequency of watchtowers reminiscent of the former Iron Curtain which is anything but a normal feature of the countryside."
He said the agreement committed the British government to the normalisation of security arrangements and the removal of security installations as soon as possible, consistent with the level of threat. "I cannot understand why the period of peace should be used to add to or extend installations that have to be dismantled if the terms of the Belfast Agreement are to be fulfilled."