The regular Diet session, which started Thursday, will be an important test for both Prime Minister Shinzo Abe and the Democratic Party of Japan leader Ichiro Ozawa. It is a prelude to local elections set for many parts of the country in April and to a watershed Upper House election in July.

For Mr. Abe, the Diet session represents the first time that lawmakers deliberate a budget drafted by his administration. At the top of his administration's agenda is education reform.

Mr. Ozawa, meanwhile, must present clear-cut alternatives to the Abe administration's policies. If he fails to prove that the DPJ can develop effective policy proposals and squarely confront the ruling Liberal Democratic Party and its coalition partner Komeito, the No. 1 opposition party will face an uphill battle in the Upper House election.