The SNP said it was on target to recruit an extra 1,000 officers
The number of police officers in Scotland has fallen from 16,266 to 16,221, a drop of 45 since the SNP entered into government.
Labour said this was a "damning indictment" of the party's policy on police recruitment.
But Justice Minister Kenny MacAskill claimed it was because of the large number of police officers retiring.
He said the Scottish Government was still on target to recruit an extra 1,000 officers by 2011.
Mr MacAskill said 52 new police officers had just completed their training and another 98 would be recruited this year:
The government also said the number of officers had gone up if part-time officers were included.
Labour leader Wendy Alexander said: "This is a damning indictment of the SNP's policy on police recruitment.
"We keep on being told about officers in training, but the facts speak for themselves. There are now less officers than there were a year ago.
"Kenny MacAskill has to admit that his policy is in tatters and he should come to parliament and explain what he will do to address his failures."
She claimed Labour had increased police numbers by 1,500 while in power and supported both police and communities across Scotland.
Ms Alexander also said the Tories must be feeling "a bit sick" after Annabel Goldie's party had claimed a victory at securing the pledge for 1,000 additional police in exchange for supporting the Nationalists' budget.
She said: "The concession they won appears not to be worth the paper it was printed on."
But Tory justice spokesman Bill Aitken said the government had until 2011 to make sure the extra officers were delivered.
"We will hold them to that pledge," he said.
SNP backbencher Stuart McMillan branded Labour's claims "bogus".
He said: "Every new police officer recruited under this SNP government is one more than there would have been with Labour in power,.
"Labour had no plans to increase the number of police in Scotland's communities, whereas the SNP are recruiting 1,000 additional officers with 150 extra recruits signing on last year."
The Liberal Democrat's Margaret Smith MSP said the numbers issue was "old news" and Labour needed to catch up.
She added: "Liberal Democrats warned that this government was recruiting the lowest number of police since the creation of the Scottish Parliament way back in January.
"The SNP, supported by their Tory buddies, have been exposed as letting down communities across Scotland."
A Scottish Government spokesman said many officers were due to retire from Strathclyde Police, the country's biggest force, when the SNP came to power.
But the force last month backed plans to increase numbers, as did Grampian.