TOKYO — Japan's Liberal Democratic Party marked its 50th anniversary Tuesday by unveiling a proposed revision to the country's pacifist constitution that would end the ban on having a military and give the armed forces a more assertive international role.

Prime Minister Junichiro Koizumi, addressing party loyalists assembled at a Tokyo hotel, credited the LDP with guiding Japan through a half-century of peace and prosperity. The LDP has ruled Japan almost continuously since its founding in November 1955.

But Koizumi urged Japan to match its weight as the world's second biggest economy by cooperating more with the international community, a reference to the LDP's planned overhaul of the constitution. "We need to take up the challenges of strife and conflict that may face international society over the next 50 years," Koizumi said.

Japan's constitution — drafted by U.S. occupation forces after World War II and unchanged since 1947 — bars the country from employing military force in international disputes and prohibits it from having a military for warfare.