Japan's parliament has passed a bill that sets out steps for holding a referendum on revising the country's pacifist constitution.
Many in Japan support the country's pacifist stand-point
The legislation was passed by the parliament's upper house, having cleared the lower house last month.
The move marks a victory for Prime Minister Shinzo Abe, who has made revising the constitution one of his top priorities, correspondents say.
The current constitution has not been changed since 1947.
Drawn up by the US occupation authorities after WWII, it bans military force in settling international disputes and prohibits maintaining a military for warfare.
But Mr Abe wants Japan to be more assertive on the world stage, with a military able to take part in peacekeeping missions abroad.
Mr Abe's ruling Liberal Democratic Party (LDP) is working on a draft of a new constitution.
The legislation passed by parliament says that a referendum on the issue cannot take place before 2010, and needs approval from a majority of voters.
Japan's troops already participate in some international missions
"Since this will take effect in three years, what is important is to deepen the debate among the people even further," Chief Cabinet Secretary Yasuhisa Shiozaki said.
Public opinion in Japan on the issue also appears to be mixed, with many in favour of some changes to the constitution while wanting the country to remain officially pacifist.
Four opposition groups - including the main opposition Democratic Party of Japan (DPJ) - opposed the bill because of divided public sentiment on the issue, Japan's Kyodo news agency said.
Critics of the proposed changes say the pacifist constitution has kept Japan out of war since the 1940s and allowed the country to focus on economic growth instead.
The move may also meet concern from South Korea and China, which remain suspicious of Japan because of its wartime aggressions.
Japan's constitution has been stretched in recent years to allow the country to have a self-defence force.
Under former Prime Minister Junichiro Koizumi, this was pushed still further, to allow troops to join peacekeeping missions in Iraq.