By Elaine Lies

TOKYO (Reuters) - Japanese Emperor Akihito, who has spent much of his time on the throne trying to heal the wounds of World War Two, intends to abdicate in a few years, public broadcaster NHK and other domestic media said on Wednesday, a step that would be unprecedented in modern Japan.

The 82-year-old monarch, who has had heart surgery and been treated for prostate cancer in recent years, expressed his intention to the Imperial Household Agency, NHK said.

It did not cite a reason and officials at the agency could not immediately be reached for comment.

Kyodo news agency, quoting a government source, said Akihito had been expressing his intention to abdicate to people around him for about a year, although in a separate report Kyodo quoted a senior Imperial Household Agency official as denying that the reports were correct.

Akihito has been cutting back on his official duties, handing over some of the burden to his heir, Crown Prince Naruhito, 56.

Born in 1933, Akihito was heir to Emperor Hirohito, in whose name Japan fought World War Two.

The soft-spoken Akihito marked the 70th anniversary of World War Two's end last year with an expression of "deep remorse", a departure from his previous remarks seen by some as an effort to cement a legacy of pacifism under threat from conservative Japanese nationalists.

"Looking back at the past, together with deep remorse over the war, I pray that this tragedy of war will not be repeated and together with the people express my deep condolences for those who fell in battle and in the ravages of war," he said.

While Akihito's father was a controversial figure, Akihito "was the first post-war emperor to embrace the (pacifist) constitution and his role as a symbol of national unity", said Koichi Nakano, a political science professor at Sophia University in Tokyo.

"He cares a great deal about war issues and reconciliation (with Asian countries). Naruhito has made clear that he will carry on with that," Nakano added.

Akihito has sought to deepen Japan's ties with the world through visits abroad. In 1992 he became the first Japanese monarch in living memory to visit China, where bitter memories of Japan's past military aggression run deep.

Emperor Kokaku, who gave up the throne in 1817, was the last Japanese emperor to abdicate, NHK said.

Miiko Kodama, a professor emeritus at Musashi University, said the Imperial Household Law would need to be amended to allow Akihito to step down, a process that could take time and debate in parliament.

A scientist by avocation, Akihito is the first royal heir to have married a commoner, Michiko Shoda, the daughter of a wealthy industrialist.

Under the U.S.-drafted, postwar constitution, Japan's emperor is "the symbol of the State and of the unity of the People", with no political power.

Akihito's efforts to draw the imperial family closer to the people in image, if not in fact, have played into a carefully crafted picture of a "middle-class monarchy" that has helped shield it from the harsh criticism suffered by flashier royals abroad.

(Additional reporting by Linda Sieg, Ritsuko Ando and Nobuhiro Kubo; Writing by William Mallard; Editing by Nick Macfie)