Akihito’s father, Hirohito, died in 1989 — Year 64 of his reign — as both the Cold War and Japan’s economic boom years were drawing to a close, intensifying the sense of a historical shift.

Akihito effectively asked Parliament to change the rules, though he could only do so in the most indirect words. His circumlocution was intended to avoid seeming to meddle in politics, which has been forbidden to Japan’s emperors since the country’s defeat in World War II, waged in Hirohito’s name.

After the war, Hirohito stunned his subjects by declaring that he was not a god, overturning decades of government propaganda and centuries of loosely held tradition. A new Constitution, imposed by the victorious United States, stripped him of political power and relegated the monarchy to a purely ceremonial role.

If Parliament grants Akihito’s wish to abdicate, it would be the biggest transformation of the Japanese monarchy since the war.

“Historically, it was extremely common for emperors to abdicate,” said Takeshi Hara, an authority on the imperial family at the Open University of Japan. More than half of Japan’s monarchs have vacated the throne, often for quiet retirement at Buddhist monasteries. Only in the 19th century, when Japan’s leaders created the cult of emperor worship, did quitting become impossible.

Prime Minister Shinzo Abe, in a short response after the address, suggested that his government was open to changing the law, though he stopped short of making a specific commitment to do so. Commentators said his vagueness, too, was intended to sidestep the Constitution’s ban on royal involvement in politics.

“Considering His Majesty’s age, the burden of his official duties and his anxieties, we must think carefully about what can be done,” Mr. Abe said.

Akihito maintains an often punishing schedule, despite treatment for prostate cancer in 2003 and heart surgery in 2012. He and his wife, Empress Michiko — the first commoner to marry into the imperial family — have become consolers in chief for victims of natural disasters, like the earthquake and tsunami that devastated parts of northern Japan in 2011.

In February, they visited the Philippines, one of numerous foreign trips intended to make amends for Japan’s depredations during the war. Akihito was the first Japanese monarch to visit China, another wartime adversary, in 1992.

In recent years some have come to see Akihito as a quiet but powerful guardian of Japan’s postwar pacifist identity, even as Mr. Abe’s conservative government has sought to loosen decades-old legal restrictions on the military.

In his address, Akihito referred several times to the postwar Constitution and the symbolic nature of the modern monarchy. He said he wanted to secure that monarchy for the future “in the midst of a rapidly aging society” and “in a nation and in a world which are constantly changing.”

Though he did not use the word abdication, he made specific arguments for allowing it. Under existing law, the crown prince could serve as regent if his father became too ill, standing in for the emperor in all but name. But Akihito indicated he did not wish to be a monarch who “continues to be the emperor till the end of his life, even though he is unable to fully carry out his duties.”

He alluded to the last imperial transition nearly three decades ago. His father had intestinal cancer during the final years of his life, and his slow, painful decline was a focus of intense attention from the public and the news media.

Akihito said he wanted to avoid a situation where “society comes to a standstill” before his death, and the elaborate funeral rites required afterward distracted from the enthronement of his heir.

• Except for diplomatic functions, his birthday and an annual speech to open Parliament, Emperor Akihito of Japan rarely speaks in public. He addressed the country on television only once, in 2011, rekindling memories of his father’s fateful broadcast in 1945.

• WWII Surrender

  In his first radio broadcast, Emperor Hirohito, the father of the current emperor, announced that Japan had been defeated in World War II. Many Japanese bowed or kneeled as they heard the monarch’s voice for the first time.

• Fukushima

  An earthquake and tsunami devastated the northeast coast of Japan in 2011, causing the world’s second-worst nuclear disaster after Chernobyl. Emperor Akihito took the unprecedented step of trying to reassure the nation in a televised address.

Opinion surveys conducted by the Japanese news media suggest that the public supports Akihito’s wish to abdicate. As many as 85 percent of respondents, depending on the survey, say they favor amending the Imperial Household Law to allow it.

“We speak respectfully about the emperor, but arguably we use him like a slave,” said Daisuke Kodaka, 34, an employee at a cosmetics company in Tokyo. “He’s our symbol, but as a person he doesn’t have human rights. We should recognize his rights.”

While Mr. Abe would be hard-pressed to deny him, an amendment process could prove awkward for Mr. Abe’s government.

“This opens other cans of worms,” said Kenneth Ruoff, the director of the Center for Japanese Studies at Portland State University and the author of “The People’s Emperor,” a history of the postwar Japanese monarchy.

Many see the Imperial Household Law as outdated in other ways, particularly regarding gender. The law says only men can inherit the throne, a provision that is increasingly in dispute. A decade ago, during a debate about whether the law should be changed to open the way for female monarchs, conservatives in Mr. Abe’s right-leaning Liberal Democratic Party were firmly opposed.

Today, Mr. Abe’s government has embraced the idea of female empowerment in other areas, notably in the workplace, but few think it is ready to extend the concept to the monarchy.

Prince Naruhito has a daughter, and his younger brother has two daughters and a son, Prince Hisahito, the only male in the youngest royal generation. Hisahito’s birth, in 2006, put an end to the debate about female monarchs, at least for the time being. But with so few males in the family, experts say the succession is far from secure for the future.

Naruhito “represents continuity” with Akihito in terms of personality and priorities, Professor Ruoff said. Like his father, he has taken up social causes, notably access to clean water in poor countries.

One issue, whatever the timing of the succession, will be the public role of Naruhito’s wife, Masako, a Harvard- and Oxford-educated former diplomat who has chronic depression, which has kept her secluded for much of the last 15 years.

In 2004, Naruhito appeared to blame the strictures of imperial life for Masako’s illness, saying unnamed antagonists had sought to “deny Masako’s career and personality.” How the experience might inspire him, as emperor, to try to change the highly insular monarchy is unclear.

Professor Ruoff said Akihito’s biggest achievement had been to focus attention on social welfare causes. When Japan hosted the Summer Olympics in 1964, Akihito became the patron of the then-obscure Paralympics. At the time, people with disabilities were often shunned and stigmatized in Japan.

“Akihito and Michiko have spent a tremendous amount of time leveraging their prestige on behalf of the least privileged members of Japanese society,” Professor Ruoff said. “I wouldn’t go so far as to say they are the conscience of the nation, but they do draw attention to these issues.”