Mr Bruton said Department of Justice figures showed that only two extra gardaí were recruited to Dublin in 2005.
Mr McDowell accused him of being a “fraud” and of knowingly producing “grossly misleading and falsified” figures.
“I am going to call on him to go to the Dáil and put down a motion, square up to me man-to-man on this issue and I will win the debate hands down.
“I am happy to take him on in Dáil Eireann any time he wants. This type of gutter politics won’t get him anywhere.”
The minister said an additional 700 gardaí had been appointed nationwide since he came to office in 2002.
He said that, of these, 278 gardaí had been recruited to the Dublin Metropolitan Region (DMR).
He said the current strength of the force stood at 12,445, of which 3,794 were based in the DMR.
Mr Bruton published figures supplied to him by Mr McDowell in an answer to a parliamentary question (PQ).
The Fine Gael deputy leader said these figures showed that the strength of the force increased from 3,740 at the end of December 2004 to only 3,742 at the end of December 2005.
But Mr McDowell said these figures were a “fraudulent abuse” of the information he provided. He claimed Mr Bruton had chosen particular time periods which failed to take into account the stages involved in recruiting gardaí.
The minister said the PQ showed that, as of November 28, 2005, there was a national strength of 12,299 and a DMR strength of 3,847.
A spokeswoman for the minister later explained the drop of 50 gardaí from the DMR since November 2005 was due to the establishment of a special gun crime unit in the National Bureau of Criminal Investigation and retirements.
Mr McDowell said his record compared favourably against the “pitiful performance” of the Rainbow coalition which preceded the first FF-PD coalition in 1997.
He said that since then garda numbers had jumped by 16.3%.
He said Mr Bruton, along with Fine Gael leader Enda Kenny and Labour leader Pat Rabbitte, sat at the Cabinet table during the Rainbow government.
“Deputy Bruton is knee high to me in terms of anything he has done for this country, he said.
He also criticised Mr Bruton’s comments that crime detection rates were very low. Mr Bruton said department figures showed that 85% of burglaries, 65% of thefts and 44% of serious assaults went undetected.
Mr McDowell said detection rates were very high, but there was a problem in relation to burglaries.