TOKYO (Reuters) - More than 450 mostly Western scholars have urged Prime Minister Shinzo Abe to confront boldly Japan's wartime past, the latest sign that the conservative leader has not erased concern that he wants to dilute past apologies.

During a high-profile trip to the United States last month, Abe expressed "repentance" over Japan's role in World War Two in a speech to Congress. But the scholars' letter suggests his public contrition has not eased foreign misgivings.

Japan's wartime legacy haunts ties with neighbors, in particular China and South Korea, and the 70th anniversary of the war's end in August has focused attention on the issue and on Abe's bid to adopt a more assertive defense policy.

The scholars, including two Pulitzer Prize-winning historians, called in a letter for Abe to address Japan's "history of colonial rule and wartime aggression", including the issue of "comfort women", as those forced to work in wartime military brothels are euphemistically known in Japan.

"As scholars of Japan and of Japan's place in the world, our collective responsibility rests on fostering open discussions ... and in leaving an honest record of its past for current and future generations," University of Connecticut professor Alexis Dudden, one of two coordinators of the project, told Reuters in an email.

Abe said during his U.S. visit he would uphold past apologies but has also repeatedly said he wants to issue a forward-looking statement to mark the anniversary of the war's end.

Many of his conservative allies think Japan has apologized enough.

One of them, Abe special aide Koichi Hagiuda, said the outline of the premier's anniversary comments on history had been set in his speech to Congress and at an April conference in Indonesia. "There won’t be a big change," he told Reuters.

The wording of Abe's anniversary statement could affect a thaw in Sino-Japanese relations and prospects for improved ties with South Korea, where the issue of "comfort women" is a major irritant.

Abe said in America his heart ached for the women's suffering and that he stood by a 1993 statement acknowledging authorities' involvement in coercing them.

Many Japanese conservatives, though, say the women were prostitutes and there was no evidence that Japan's military or government were directly involved in forcing them.

The scholars criticized such "legalistic arguments".

"This year represents an opportunity for the government of Japan to show leadership in addressing Japan's history of colonial rule and wartime aggression in both words and action," they said.

(Editing by Robert Birsel)