Australia currently has 300 soldiers in Afghanistan, working as part of the Dutch-led Nato reconstruction team.
The new troops are to begin arriving in late July and the deployment would be completed over a two-year period, Howard told reporters.
Australia originally had sent 150 Special Forces troops to Afghanistan as part of the US-led war that expelled the Taliban and al-Qaida forces in late 2001.
It gradually reduced its troop commitment to just one soldier, but began increasing its military presence again last year, sending 190 elite forces to help stem a rising tide of insurgent-led violence ahead of the September's landmark elections.
Last month, Canberra announced it would also send an extra 110 troops and two helicopters to Afghanistan - bringing its total troop commitment to 300.
Howard said the new Australian contingent would be a mixed security and reconstruction task force and would be focused in the volatile southern province of Uruzgan, known as a Taliban stronghold.
Fighters loyal to the toppled Islamist regime have renewed attacks in recent months, increasingly using suicide bombings against international forces and the Afghan authorities.
Nato is preparing to expand its
presence in Afghanistan
The announcement comes as Nato prepares to expand its peacekeeping mission from 9000 to about 16,000 troops in Afghanistan, to become responsible for security in about three-quarters of the country.
The separate US-led combat force will keep the lead role in the eastern sector where Taliban holdouts have been most active.
Australia, a staunch US ally, also maintains about 1320 troops in and around Iraq, including about 460 soldiers guarding Japanese reconstruction teams in the southern province of al-Muthanna.
Howard said he was confident that the new deployment would not overstretch the capacity of Australia's defence forces.