TOKYO (Reuters) -- Japan's opposition Democratic Party on Sunday threw down a gauntlet to the ruling camp ahead of an expected November election, showcasing a manifesto that includes pledges requiring all political donations to be made public and also plans to abolish a controversial public highway corporation.

"We will definitely achieve a change in government to change Japan's politics," Democratic Party chief Naoto Kan told a convention held to formally unveil its policy pledges.

Popular Prime Minister Junichiro Koizumi is expected to dissolve Parliament's Lower House on Friday and call an election for November 9 in hopes of securing a big win for his ruling coalition and a fresh mandate for his economic reform agenda.

The pro-reform Democrats have struggled to boost their profile as Koizumi grabbed the spotlight with his battle against his own Liberal Democratic Party's (LDP) old guard, but argue that the LDP's vested interests make it incapable of reform.

The Democrats hope their concrete policy pledges and a merger with a smaller party will persuade voters they are a viable alternative to the long-ruling LDP.

The LDP-led ruling camp holds 285 seats in the 480-seat Lower House. The Democratic Party has 138 seats compared to the 244 held by the LDP alone, according to Lower House data.

Koizumi, who took office in 2001, has said a one-page platform he announced ahead of his re-election as LDP president last month will be the core of the party's campaign pledges.

But the LDP has not yet unveiled a formal policy statement.

The Democratic Party's pledge to require all political donations be made public was a stark contrast with an LDP proposal to raise the hurdle for donations that must be declared to 240,000 yen ($2,166) annually from 50,000 yen at present. ---Free Highways, Wildcard Candidates? ----

The Democrats' platform also pledged to abolish a public corporation in charge of highways within three years and make most highways toll-free, to cut the number of lawmakers by 10 percent and slash wasteful public works spending.

Koizumi wants to privatize the highway corporation.

But many LDP lawmakers, accustomed to building roads and bridges to woo local voters, oppose the move.

The head of the debt-ridden body was expected to resign today due to a controversy over its financial records.

The Democrats also pledged to revamp the pension system -- a growing source of voter anxiety given Japan's graying population -- and use the consumption tax to fund basic public pensions.

Opinion polls show Koizumi's support rate has surged to some two-thirds of voters since he appointed a youthful lawmaker to a top LDP post and rejected calls to ditch his pro-reform banking minister in a cabinet shakeup late last month.

One wild card in the coming election is the probable candidacy of fiery former foreign minister Makiko Tanaka, once one of Japan's most popular politicians and a close Koizumi ally who is now a potentially powerful critic of the premier. Sacked by Koizumi in January 2002, Tanaka later resigned from Parliament after allegations, repeatedly denied, that she had misused public funds intended to pay an aide's salary.

Prosecutors last week decided not to file charges in the case and Tanaka told a news conference in her northern home district of Niigata on Sunday that she was leaning toward running.

"Among my supporters there are strong calls for me to run, and I view those calls seriously," she said.