The first Diet debate on the Constitution since it was written in 1946 could come in January.

The Lower House on Tuesday got the ball rolling by passing a bill that revises the Diet Law and establishes an in-house panel to conduct the debate, which is expected to take at least five years.

The bill was supported by the ruling Liberal Democratic Party, its coalition partner the Liberal Party, New Komeito, which is being wooed by the LDP to join the coalition, and the opposition Democratic Party of Japan.

The Japanese Communist Party opposed the bill while the Social Democratic Party boycotted the balloting; the two parties believe the committee's purpose is to prepare to amend the Constitution.

Given the four other parties' backing, however, the bill is expected to become law before the close of the current Diet session in mid-August after being revised by the House of Councilors, allowing that chamber to set up its own committee on the issue.

Each house's committee is likely to be established come January, when the next ordinary session is slated to open. Article 9, which stipulates that the nation forever renounces war, is expected to be the most contentious issue.

The Constitution took effect on May 3, 1947, when Japan was under the Allied Occupation following its defeat in World War II. The nation's fundamental law document, especially Article 9, has since been considered so sacred that it has never been amended -- nor has the Diet ever set up a special panel to discuss possible amendments.

Each committees' sessions will be, in principle, open to the public, but they can be closed through a committee resolution. The panels will not be empowered to propose amendments to the Constitution. That job will be left to groups of lawmakers or the Cabinet once debate is finished.

Constitutional amendments must be approved by two-thirds of both Diet chambers and a majority of the public through a plebiscite.

The Social Democratic Party and the Japanese Communist Party are still vehemently opposed to any revisions to the war-renouncing article, but with conservative lawmakers increasing their numbers in recent years, voices calling for a review of the Constitution have grown stronger.

In fact, it was a suprapartisan group of some 350 conservative lawmakers -- from the LDP, the Liberal Party, the DPJ, New Komeito and Kaikaku Club (Reformers' Network Party) -- that submitted the bill to the Diet.

Some say Article 9 should be revised to enable the Self-Defense Forces to participate more actively in international peacekeeping activities.

In other issues, some want to allow state subsidies for private schools that are banned under the Constitution but distributed under other legislation, while others point out that the right to live in a comfortable environment and the right to know -- closely connected to freedom of information measures -- should be spelled out in the Constitution.