In a brief statement on President Mahinda Rajapakse's website on Wednesday, the government said the department of census of statistics would conduct what it called an "island-wide census to assess the loss of human life and damage to property", adding that the work would begin on November 28.
The announcement came after Rajapakse hosted a Commonwealth summit this month which was overshadowed by allegations of war crimes committed by government troops in the final stages of the conflict in May 2009.
UN bodies and rights groups have said that as many as 40,000 civilians may have died in the final phase of the conflict when the army routed the Tamil Tiger rebel movement in its last northern stronghold.
Rajapakse and his mainly ethnic Sinhalese regime have previously insisted that no civilians died in the finale to the war.
The president has also rejected any suggestion of international investigators being allowed to conduct an independent inquiry on Sri Lankan soil, saying that he would only sanction a domestic probe.
But international pressure has been steadily building and Rajapakse was sorely embarrassed when the leaders of Canada, India and Mauritius all boycotted the Commonwealth meeting in protest at Colombo's rights record.
Britain's Prime Minister David Cameron did attend the summit but he infuriated Rajapakse by paying an historic visit to the war-torn Jaffna region.
After meeting with survivors and relatives who had lost loved ones during the war, Cameron then warned that he would lead a push for an international probe unless Sri Lanka produces credible results of its own by March.
Rajapakse told his fellow leaders that the country needed more time to conduct its own investigations.
"They have to trust us," he said at the summit.
"Pressure won't do anything. ... It's much better to wait rather than demand or dictate."
While the government has previously spoken of plans to conduct a comprehensive survey, it is the first time that it has set out a timetable.
The idea was one of the recommendations of a government-appointed panel that submitted a report last year.
"The census should enable us to determine the numbers of the dead and the disappeared", Suranjana Waidyaratne, a member of the panel, told reporters late Wednesday.
More than 100,000 people are believed to have been killed during the course of the war, according to previous UN figures.
The war, one of the longest-running civil conflicts in Asia, ended when the Tamil Tiger leader Velupillai Prabhakaran was killed in his final stronghold in the northeast of the island.While Jaffna held its first provincial elections since the war in September, with the main Tamil party winning by a landslide, the vote was seen as having done little to address long-standing demands for greater autonomy.