Hundreds of elated supporters of South Korean dissident leader Kim Dae Jung crowded into his Seoul home today to celebrate a government decision to free him from house arrest and restore the political rights of 13 other opposition figures.

Plainclothesmen blocking access to Kim's house withdrew at 10 a.m. and gave supporters their first chance to meet with him since his return from self-imposed exile one month ago.

As well-wishers and reporters looked on, Kim embraced Kim Young Sam, with whom he shares leadership of the opposition movement.

Their next political step remains unclear. But the two men said they would put aside their past rivalries and work together to "restore democracy" in South Korea.

President Chun Doo Hwan's decision to ease restrictions on the two Kims and the other leaders is the latest in a series of cautious concessions he has made to the opposition.

The move comes three weeks after a new opposition party loyal to the Kims swept South Korea's cities in National Assembly elections. The ruling Democratic Justice Party retained its majority but was dealt a heavy psychological blow.

In addition, Chun's move coincides with his preparations for a meeting with President Reagan in Washington in April. Chun is particularly anxious to project abroad an image of flexibility and reform.

A government statement issued today said that a new stability is prevailing in South Korea. But it warned against reversion to what it called old-style politics of "corruption, demagoguery, violence and intrigue."

Although Kim today was free to come and go in the city for the first time in five years, the government stopped short of restoring his political rights.

He will remain under tight police surveillence. He will be free to address small groups of people, government officials said today, but not to hold party office or to form political organizations.

Kim was convicted of sedition by a military court in 1980. Two years later, the government suspended his 20-year sentence and allowed him to go into exile in the United States. After his return to Seoul last month, he was put under house arrest.

It remains to be seen, however, if these restrictions on Kim will have any real meaning. Without leaving his home today, Kim demonstrated that it is possible to hold considerable political power in South Korea without holding formal office.

The government's new tolerance was also reflected in this afternoon's newspapers. They reported the two Kims' meeting with banner headlines and large photos.

Readers here could not remember seeing a picture of Kim Dae Jung in South Korea's tightly regulated press since 1980.

Using an emergency law, Chun banned a total of 567 people that year, but in stages lifted the bans until only 14 people, including the two Kims, were still covered when last month's elections were held.

A government order issued today formally lifted all remaining bans. However, it said that, with Kim Dae Jung still living under a suspended sentence, other laws would bar him from holding political office.

This afternoon, Kim sat on a carved wooden easy chair in his living room and received group after group of visitors, many of them displaying gifts of flowers and a deference almost suitable for royalty.

In an interview, Kim said that he would wait a bit before making his next move. "I will be watching the government attitude for a while. I will not be short-tempered," he said.

He said he was discouraging his supporters from staging demonstrations, so as to foster an atmosphere in which he and other opposition leaders could have a dialogue with Chun.

He criticized the government for failing to restore his full rights. But he said that open participation of the 13 others would be "an important change."