Minister for Justice Michael McDowell said he had no recollection of reading the file relating to Olukunle Elukanlo, whose deportation order he revoked.
He revealed that the cost of providing asylum services across several departments last year was €370 million.
Mr McDowell said his general practice was to read and consider the summary of some cases, or to read and consider the entire file in exceptional cases.
"The approach I have outlined is the only realistic way of dealing with the volume of cases fairly and efficiently."
This, he said, was in accordance with the "Carltona principle" which recognised that the system of departmental organisation was based on the view that ministers responsible to parliament would ensure that important duties were committed to experienced officials.
The Minister was replying to Labour spokesman Joe Costello, who urged him to refrain from "sending gardaí into classrooms".
Mr McDowell said the volume of such files could be understood from the fact that since January 2001, 10,200 deportation orders had been signed by him or his predecessor. Last year, the number of individual cases varied from 10 to 20 on each working day, which was the result of the Government's asylum-processing strategies and the commitment of resources to the area.
"In the light of the volume of deportations filed, it is unrealistic to think it possible that I or any other minister for justice could remember the precise details of every case."
Mr McDowell said that if he had a system whereby people with children of an age to be in primary or secondary education would be effectively immune from deportation until both educational cycles were completed, 50 per cent of family asylum-seeking groups in Ireland would be exempt from deportation.
He said some 18,000 applications to reside in the State on the basis of parentage of an Irish-born child were made before the March 31st deadline under the relevant scheme. About 3,000 of that number have been granted leave to remain.
