The troops are in addition to a 240-member task force promised in May to join a Netherlands-led provincial reconstruction team in Afghanistan's southern Uruzgan province from next month, Howard told Parliament, the AP reports.
He said the task force would be bolstered with 30 soldiers to "enhance the security, robustness and flexibility of the task force."
An additional infantry company group of 120 soldiers equipped with armored personnel carriers would also be sent to safeguard the task force, he said.
The task force will be sent for two years and the level of security would be reassessed after six months, Howard said.
Australia already has 300 troops in Afghanistan, including 190 special forces soldiers sent last September to bolster security for elections that month.
Opposition Labor Party Leader Kim Beazley welcomed the military commitment and accused the government of withdrawing troops too soon after the fall of the Taliban almost five years ago.
More than 900 people have died in Afghanistan since May, most of them suspected militants killed by international or Afghan troops.