KYOTO, Japan: For Japan, the crowning of Hiromu Nonaka as its top leader would have been as significant as America’s election of its first black president.

Despite being the descendant of a feudal class of outcasts, who are known as buraku and still face social discrimination, Nonaka had dexterously occupied top posts in Japan’s governing party and served as the government’s No. 2 official. The next logical step, by 2001, was to become prime minister. Allies urged him on.

But not everyone inside the party was ready for a leader of buraku origin. At least one, Taro Aso, Japan’s current prime minister, made his views clear to his closest associates in a closed-door meeting in 2001.

“Are we really going to let those people take over the leadership of Japan?” Aso said, according to Hisaoki Kamei, a politician who attended the meeting.

Mr. Kamei said he remembered thinking at the time that “it was inappropriate to say such a thing.” But he and the others in the room let the matter drop, he said, adding, “We never imagined that the remark would leak outside.”

But it did — spreading rapidly among the nation’s political and buraku circles. And more recently, as Aso became prime minister just weeks before President-elect Barack Obama’s victory, the comment has become a touchstone for many buraku.

How far have they come since Japan began carrying out affirmative action policies for the buraku four decades ago, mirroring the American civil rights movement? If the United States, the yardstick for Japan, could elect a black president, could there be a buraku prime minister here?

The questions were not raised in the society at large, however. The topic of the buraku remains Japan’s biggest taboo, rarely entering private conversations and virtually ignored by the media.

The buraku — ethnically indistinguishable from other Japanese — are descendants of Japanese who, according to Buddhist beliefs, performed tasks considered unclean. Slaughterers, undertakers, executioners and town guards, they were called eta, which means defiled mass, or hinin, nonhuman. Forced to wear telltale clothing, they were segregated into their own neighborhoods.

The oldest buraku neighborhoods are believed to be here in Kyoto, the ancient capital, and date back a millennium. That those neighborhoods survive to this day and that the outcasts’ descendants are still subject to prejudice speak to Japan’s obsession with its past and its inability to overcome it.

Yet nearly identical groups of outcasts remain in a few other places in Asia, like Tibet and Nepal, with the same Buddhist background; they have disappeared only in South Korea, not because prejudice vanished, but because decades of colonialism, war and division made it impossible to identify the outcasts there.

In Japan, every person has a family register that is kept in local town halls and that, with some extrapolation, reveals ancestral birthplaces. Families and companies widely checked birthplaces to ferret out buraku among potential hires or marriage partners until a generation ago, though the practice has greatly declined, especially among the young.

The buraku were officially liberated in 1871, just a few years after the 13th Amendment abolished slavery in the United States. But as the buraku’s living standards and education levels remained far below national averages, the Japanese government, under pressure from buraku liberation groups, passed a special measures law to improve conditions for the buraku in 1969. By the time the law expired in 2002, Japan had reportedly spent about $175 billion on affirmative action programs for the buraku.

Confronting Prejudice

Fumie Tanaka, now 39, was born just as the special measures law for the buraku went into effect. She grew up in the Nishinari ward of Osaka, in one of the 48 neighborhoods that were officially designated as buraku areas.

At her neighborhood school, the children began learning about discrimination against the buraku early on. The thinking in Osaka was to confront discrimination head on: the problem lay not with the buraku but with those who harbored prejudice.

Instead of hiding their roots, children were encouraged to “come out,” sometimes by wearing buraku sashes, a practice that Osaka discontinued early this decade but that survives in the countryside.

Sheltered in this environment, Tanaka encountered discrimination only when she began going to high school in another ward. One time, while she was visiting a friend’s house, the grandparents invited her to stay over for lunch.

“The atmosphere was pleasant in the beginning, but then they asked me where I lived,” she said. “When I told them, the grandfather put down his chopsticks right away and went upstairs.”

A generation ago, most buraku married other buraku. But by the 1990s, when Tanaka met her future husband, who is not a buraku, marriages to outsiders were becoming more common.

“The situation has improved over all,” said Takeshi Kitano, chief of the human rights division in Osaka’s prefectural government. “But there are problems left.”

In Osaka’s 48 buraku neighborhoods, from 10 to 1,000 households each, welfare recipient rates remain higher than Osaka’s average. Educational attainment still lags behind, though not by the wide margins of the past.

What is more, the fruits of the affirmative action policies have produced what is now considered the areas’ most pressing problem: depopulation. The younger buraku, with better education, jobs and opportunities, are moving out. Outsiders, who do not want to be mistaken for buraku, are reluctant to move in.

By contrast, Tokyo decided against designating its buraku neighborhoods. It discreetly helped buraku households, no matter where they were, and industries traditionally dominated by buraku groups. The emphasis was on assimilation.

Over time, the thinking went, it would become impossible to discriminate as people’s memory of the buraku areas’ borders became fuzzier. But the policy effectively pushed people with buraku roots into hiding.

In one of the oldest buraku neighborhoods, just north of central Tokyo, nothing differentiates the landscape from other middle-class areas in the city. Now newcomers outnumber the old-timers. The old-timers, who all know one another, live in fear that their roots will be discovered, said a 76-year-old woman who spoke on the condition that neither she nor her neighborhood be identified.

“Me, too, I belong to those who want to hide,” she said. “I’m also running away.”

A Politician’s Roots

Nonaka is one of the rare politicians who never hid his buraku roots. In 2001, he was considered a leading contender to become president of the long-governing Liberal Democratic Party and prime minister.

Now 83, he was born into a buraku family from a village outside Kyoto. On his way home at the end of World War II, he considered disappearing so that he would be declared dead, he once wrote. With the evidence of his buraku roots expunged, he had thought, he could remake himself in another part of Japan, he wrote.

Nonaka eventually entered politics, and, known for his fierce intelligence, he rose quickly. By 2001, he was in a position to aim for the prime ministership. But he had made up his mind not to seek the post. While he had never hidden his roots, he feared that taking the top job would shine a harsh spotlight on them. Already, the increasing attention had hurt his wife, who was not from a buraku family, and his daughter.

“After my wife’s relatives first found out, the way we interacted changed as they became cooler,” Nonaka said in an interview in his office in Kyoto. “The same thing happened with my son-in-law. So, in that sense, I made my family suffer considerably.”

But rivals worried nonetheless. One of them was Aso, now 68, who was the epitome of Japan’s ruling elite: the grandson of a former prime minister and the heir to a family conglomerate.

Inside the Liberal Democratic Party, some politicians gossiped about Nonaka’s roots and labeled some of his closest allies fellow buraku who were hiding their roots.

“We all said those kinds of things,” recalled Yozo Ishikawa, 83, a retired lawmaker who was allied with Aso.

“That guy’s like this,” Ishikawa said, lowering his voice and holding up four fingers of his right hand without the thumb, a derogatory gesture indicating a four-legged animal and referring to the buraku.

And so, at the closed-door meeting in 2001, Aso made the comment about “those people” in a “considerably loud voice,” recalled Kamei, the politician. Kamei, now 69, had known Aso since their elementary school days and was one of his biggest backers.

Aso’s comment would have stayed inside the room had a political reporter not been eavesdropping at the door — a common practice in Japan. But because of the taboo surrounding the topic of the buraku, the comment was never widely reported.

Two years later, just before retiring, Nonaka confronted Aso in front of dozens of the party’s top leaders, saying he would “never forgive” him for the comment. Aso remained silent, according to several people who were there.

It was only in 2005, when an opposition politician directly questioned Aso about the remark in Parliament, that Aso said, “I’ve absolutely never made such a comment.”

The prime minister’s office declined a request for an interview with Aso. A spokesman, Osamu Sakashita, referred instead to Aso’s remarks in Parliament.

In the end, Nonaka’s decision not to run in 2001 helped a dark-horse candidate named Junichiro Koizumi become prime minister. Asked whether a Japanese Obama was now possible, Nonaka said, “Well, I don’t know.”

Hopes for the Future

That is also the question asked by many people of buraku origin recently, as they waver between pessimism and hope.

“Wow, a black president,” said Yukari Asai, 45, one of the two sisters who owns the New Naniwa restaurant in Osaka’s Naniwa ward, in Japan’s biggest buraku neighborhood, reflecting on Obama’s election. “If a person’s brilliant, a person’s brilliant. It doesn’t matter whether it’s a black person or white person.”

After serving a bowl of udon noodles with pieces of fried beef intestine, a specialty of buraku restaurants, Asai sounded doubtful that a politician of buraku origin could become prime minister. “Impossible,” she said. “Probably impossible.”

Here in Kyoto, some had not forgotten about Aso’s comment.

“That someone like that could rise all the way to becoming prime minister says a lot about the situation in Japan now,” said Kenichi Kadooka, 49, who is a professor of English at Ryukoku University and who is from a buraku family.

Still, Kadooka had not let his anger dim his hopes for a future buraku leader of Japan.

“It’s definitely possible,” he said. “If he’s an excellent person, it’s just ridiculous to say he can’t become prime minister because he just happened to be born a buraku.”