By Tetsushi Kajimoto and Tomasz Janowski

TOKYO (Reuters) - Japan's ruling party vowed on Tuesday to defend the nation's interests with "cool-headed and practical" diplomacy in an election manifesto that sought to portray a contrast with the hawkish rhetoric of its main opposition rivals.

The Democratic Party of Japan (DPJ) also reiterated its goal of phasing out nuclear power by the 2030s -- another policy where it differs with the Liberal Democratic Party (LDP), which advocates further debate before deciding on Japan's energy mix.

While affirming their commitment to end deflation and achieve growth targets similar to those adopted by the LDP, the Democrats stopped short of prescribing a new inflation goal for the Bank of Japan or suggesting changes to central bank law.

The LDP, led by former Prime Minister Shinzo Abe, tops opinion polls with 22-25 percent of voters saying they will cast their ballots for the once-dominant party. That is about 10-15 points ahead of the Democrats, who have struggled to close the gap since Prime Minister Yoshihiko Noda called earlier this month for a snap election on December 16.

The Democrats swept to power in 2009 promising to change how the country is run after more than half a century of nearly non-stop LDP rule characterized by cozy ties between the powerful bureaucracy, big business and ruling party lawmakers. But support for the DPJ has plummeted since them due to policy flip-flops and internal bickering.

Abe, 58, has grabbed headlines with his calls for reversing a long decline in Japan's defense spending and toughening Tokyo's stance in a territorial row with Beijing over an island chain that Japan controls, but that both China and Taiwan claim.

The DPJ took a less confrontational line.

"To protect the people's lives and assets is the most important role of the government. By combining 'cool-headed diplomacy' with 'responsible defense' and deepening the U.S.-Japan alliance, we will ensure defense," its platform said.

The LDP has suggested posting Japanese personnel on the uninhabited islets to reassert Japan's control, a step that Noda has warned risks further escalating tensions with China.

Sino-Japanese ties soured after the Japanese government bought the disputed East China Sea islets in September in an ill-fated effort to forestall a deeper crisis by scuppering an alternative plan floated by the nationalist Tokyo governor.

Seen in Beijing as a nationalization of private property, it sparked violent protests and a boycott of Japanese goods. Chinese ships were dispatched to patrol disputed waters.

The rocky, uninhabited islets, called Senkaku in Japan and Diaoyu in China, are located near rich fishing grounds and potentially huge oil and gas reserves.

TRADE PACT BURIED IN FINE PRINT

Contrary to some speculation that Noda could make Japan's possible participation in the U.S. led Trans-Pacific Partnership trade pact a leading campaign issue, the issue got buried in the fine print of its economic pledges - a reflection of internal opposition to Noda's backing for joining the pact.

The document said that while the party would pursue the TPP and other trade agreements, it would be up to the government to make final decisions.

"In doing so, we will make sure to protect Japan's agriculture, food safety and universal health-care system based on a premise to protect national interests."

Those economic pledges included efforts to end deflation by the fiscal year starting April 2014 and achieving nominal economic growth of 3 percent a year on average in the years to 2020.

Abe and his party have adopted similar targets, but also called for "unlimited" monetary easing, adopting a 2 percent inflation target, double the existing one, and changes to the BOJ charter to broaden its policy brief to jobs and growth.

In a TV appearance on Sunday, Noda called Abe's thinking "dangerous" and said it would undermine central bank independence if the government lays out its policy goals. The Democrats' manifesto refrained from prescribing specific policies for the BOJ.

"The government and the Bank of Japan work together to do the utmost to beat deflation based on a joint statement they issued for the first time in October 2012." it said.

(Additional reporting by Kaori Kaneko; Editing by; Raju Gopalakrishnan)