Most speak Japanese perfectly. They favor no distinctive dress or hair style and, racially, their features are similar to the Japanese. At first meeting, it is difficult to recognize them as foreigners at all.

Still, the 670,000 Korean nationals who live permanently in Japan are a people in between. Neither Korean nor Japanese, they are excluded from much of their adopted country's steadily growing prosperity.

As the only significant foreign minority in a country that takes pride in homogeneity, these Koreans are in the spotlight today as Japan prepares to receive South Korean President Chun Doo Hwan, the first Korean head of state to make an official visit here.

High among Chun's objectives here will be better treatment for his compatriots. While a few have become wealthy in Japan, more typically they work in low-paying jobs in junkyards and restaurant kitchens.

Some of their neighborhoods are among the few in Japan that can be described as slums.

Some Koreans will welcome Chun's assistance. Others are planning demonstrations against him. As in their homeland, Koreans here are sharply polarized, some committed to the pro-American South Korean government and others to Communist North Korea.

But they share a common heritage and, in many cases, a feeling of resentment. About two-thirds were born in Japan; most of them work honest jobs and pay their taxes. But still they are often denied the rights and respect that the Japanese accord each other.

"Living together with different kinds of people is a fundamental of democracy," says Rev. Hiroo Sekita, a Japanese Protestant minister who works with residents of a Korean shantytown in Kawasaki city near Tokyo. "But Japanese society is not yet mature enough to do that."

The Japanese government maintains it is working to improve the Koreans' standing and has made considerable progress.

"When we receive complaints we do our best to investigate and take any necessary action," said an official at the human rights office of the Ministry of Justice.

Koreans first came to Japan in large numbers after their country was absorbed into the Japanese empire in 1910. Farmers who lost their land to Japanese expropriation migrated, hoping for work. Others were shipped over by force to be laborers.

By government order, they took Japanese citizenship and names and learned the language.

They served in the military and worked in mines and munitions factories. About 20,000 Koreans were killed at Hiroshima. A Korean kamikaze pilot is believed to have died in the waters off Okinawa.

After Japan's surrender in 1945, Korea regained its independence and Koreans their nationality. But many chose to stay in Japan, where they had jobs, family and, their leaders concede, better financial prospects than in Korea.

Many of the expatriates hide their Korean names and identity, either out of shame or because life flows more smoothly without them. Korean children, for instance, are sometimes reluctant to bring Japanese friends home, lest a grandmother in Korean robes be seen and their background become known.

In the early 1970s, a civil rights campaign arose in Kawasaki and eventually spread all over the country. It continues today, with the goal of equal treatment with the Japanese and pride in Korean culture and beliefs. Some Koreans are insisting their Korean names go on official documents such as school registrations and city records.

From the government, Koreans have won rights to welfare payments, low-interest loans and public housing. Recently, the postal service began hiring its first Korean letter carriers, an occupation formerly reserved for Japanese.

Job discrimination in private companies continues to push many Koreans into businesses dominated by Koreans, such as restaurants and pinball parlors. Koreans say that Japanese companies often refuse outright to hire them. "Even if you get in, you will never make it to the top," says Do Hong Nam, 27, who works at a restaurant owned by his father.

Incidents arise periodically as reminders that some Japanese continue to view Koreans through colonial eyes.

Recently, the secretary general of the ruling Liberal Democratic Party, Rokusuke Tanaka, complained to Japanese reporters that the South Korean judo team unfairly used elbow jabs against Japanese competitors at the Olympics, according to press reports.

He was quoted several times muttering, "I just don't like Koreans."

Japanese stereotypes of Koreans have them picking fights on school playgrounds, smelling day and night of garlic and in general lacking good manners. Even Japanese who reject these beliefs concede that Japanese society is simply not prepared to embrace outsiders.

"We are a one-race nation," said a young travel agency employe.

Many government programs and policies work to maintain that purity. No significant immigration is allowed and people who do get in are encouraged to take Japanese names. While giving hundreds of millions of dollars to support Indochinese refugees, Japan has resettled only about 3,400 of the more than a million who have fled their countries since 1975.

Many Koreans resist assimilation. Only a few thousand take citizenship each year. "Our pride, our self-respect, do not allow us to become Japanese," says Choo Yeong Sang, chief of propaganda for a residents' association that is sympathetic to South Korea.

His organization, and a rival one oriented toward North Korea, work day and night to keep the Koreans' eyes on the homeland. They sponsor schools, cultural festivals, language classes and trips to Korea.

The pro-North Korean association, monitored closely by the Japanese police, runs a commercial bank and credit association with offices around the country.

Through them, the two governments on the Korean peninsula vie for the allegiance of the expatriates, who despite their low standing in Japanese society have money the governments want.

Pro-North Korean businessmen have presented the cash-short North with ships and complete factories, earning special designation there as "patriotic capitalists."

Koreans frequently travel to their homeland, but most say they have no plans ever to give up Japan. "I have deep roots in Japan," says Do. "I feel I'm almost Japanese, but still I know I am Korean. My patriotic feelings are there, not here."