South Korean dissident leader Kim Dae Jung appeared to be under house arrest tonight following a turbulent arrival that has sparked charges that South Korean police beat Kim and several accompanying American dignitaries.

Kim's return this morning from two years of exile in the United States prompted the largest opposition demonstration in Seoul in four years. Thousands of jubilant supporters, many of them waving his portrait and shouting his name, lined the streets from Kimpo International Airport to welcome a man who is barred from political activity here.

More than 17,000 police officers had been mobilized to maintain strict security around the airport, Kim's house and other parts of Seoul, police sources said.

After alighting from a Northwest Orient Airlines flight shortly before noon, Kim was driven by police to his house in Seoul's Dongkyo-dong district. Although reporters were later allowed into the house to see Kim, neighborhood police told him not to go out, and members of his personal staff were required to leave, Kim said.

Kim's return was further marred by a fracas with security men at the airport, who forcibly separated him and his wife from American human rights activists who had returned with them.

In Washington, a U.S. spokesman said a formal protest had been presented to South Korea concerning "the regrettable events" surrounding Kim's arrival. He said the United States asked and received assurances that the alleged mistreatment would be investigated and Kim's safety protected, a State Department spokesman said. Details on Page A15.

The four leaders of the American escort delegation, Rep. Edward F. Feighan (D-Ohio), Rep. Thomas M. Foglietta (D-Pa.), former U.S. ambassador to El Salvador Robert White and former assistant secretary of state for human rights Patricia Derian, said government se-curity men assaulted their group as they stepped off their flight, then hustled Kim into an elevator.

Journalists who had accompanied Kim on the flight from Tokyo left the plane before he did and were pushed into the terminal building before the disorder occurred.

The Korean police had asked Kim to enter a special elevator. Kim refused, saying he wished to proceed to immigration like an ordinary traveler.

The police insisted. According to Feighan, security men formed a circle around Kim, White and Foglietta. Kim and the Americans, who had agreed before the plane landed that they would accompany Kim on each step of his way home from the airport, linked arms and waited.

What happened next is subject to debate.

The four Americans say police pulled Kim away from them. They picked him up bodily and propelled him into the elevator.

"He was punched several times as he was put into the elevator and several times again in the elevator," Foglietta said later.

White said: "The security guards grabbed Mr. Kim, and Mr. Kim fought back. They punched him."

Calling the security men "a group of thugs," Derian said "they used their shoulders, their heads, their knees and elbows."

Foglietta said that during the scuffle, he, Feighan and White were all knocked to the floor of the terminal building. However, Feighan said only White was knocked down. Kim and his wife, meanwhile, were taken by the elevator to a van and driven by back roads to their house. There, Kim apparently was placed under house arrest.

The Americans then went to Kim's house and gave angry statements to reporters waiting outside.

"No one offered any kind of threat to them," White said, referring to the security police. "There was absolutely no excuse for this type of violence."

In a press conference at Kim's house later, Derian said the incident should cause the Reagan administration to rethink its invitation to South Korean President Chun Doo Hwan to visit the White House in April. The United States intervened with the South Korean government last week, extracting an assurance that Kim would not be imprisoned to finish a prison sentence. In return, Washington promised that Chun's scheduled state visit to Washington in April would go on as planned.

White contended that the incident raised questions about Seoul's ability to provide security for Americans at the 1988 Summer Olympics, which are to be held here.

The Americans, part of a 37-member delegation, had come with Kim on the flight to Seoul in the belief that their presence would help protect him from possible assassination. Everyone remembered the assassination at the Manila airport of exiled Philippine opposition leader Benigno Aquino Jr. when he returned home under similar circumstances in August 1983.

According to Derian, they had been assured that they would be allowed to accompany Kim every step of the way. "It the promise was absolute from the Korean government and the American government," she said.

Kim told reporters later at his house that he was unsure whether he actually had been struck. But Kim, who walks with a cane, said that the scuffle had created problems for a hip ailment he has.

His account of the incident was distinctly more low-key than the Americans' version. Although he condemned the incident, he said, "I have become very much familiar with the treatment of the Korean government . . . It is too early for me to be so strongly outraged," he said.

A senior South Korean government official immediately denigrated the claims of the Americans.

"Some of the delegation insisted that they go from the plane into the elevator with Mr. Kim and since it was too small, the security men pushed them back," said government spokesman Choi Tae Soon.

"But this is not beating and punching. Are they such cowards and of feminine structure? Since when have these American congressmen become like bean curd? This doesn't sound like the people who tamed the West, the pioneers," the spokesman said, according to Knight-Ridder news service.

The Seoul metropolitan police issued a statement denying that Kim had been beaten.

Security agents "merely separated Mr. Kim and his family from those accompanying them and escorted them to an elevator in order to ensure his safety," the statement said.

Korean officials also noted that The Associated Press had quoted Kim's wife, Lee Hee Ho, as saying that "there was no beating."

Later, at their hotel in Seoul, the members of the American delegation met with U.S. Ambassador Richard E. Walker. Some members of the delegation accused the embassy of failing to follow through on a guarantee that Kim's return home would be without incident.

Walker, a Republican appointee facing a predominantly Democratic group, defended his embassy's performance.

But the embassy, at the request of the two congressmen, sent a note of protest to the South Korean Foreign Ministry complaining that "force was used by security personnel." It also protested that three embassy officials who were supposed to meet the group on the plane were denied access by airport authorities.

Walker is known to have said privately that the incident was blown out of proportion and suggested that the group may have provoked the security guards' action by linking arms.

Although Kim is by far the best known opposition leader in South Korea, some members of the opposition distrust him. But his return seemed to have given the camp the spiritual boost it had hoped for. Kim's standing among the 40 million South Koreans remains unclear. Still, his return was a rare flash of triumph in Kim's political career, which has run the gamut of prison, exile and media blackouts for the past 12 years.

As one of 15 politicians still under political ban by the Chun government, Kim's name almost never appears in the press.

Yet, thousands of people gathered at and around the airport today to try to catch a glimpse of the man. The U.S. Embassy cited estimates that the crowd numbered 15,000.

Other opposition leaders, such as Kim Young Sam, Kim Dae Jung's old rival for leadership of the movement, were prevented by police from attending the welcoming ceremony. But others jostled their way through and gave brief speeches in front of Kimpo's arrival lounge.

Outside the airport grounds, white cloth flags bearing the politician's photograph and the message "cheers for the return of Kim Dae Jung" were displayed prominently. Banners were unfurled.

In places, the crowd seemed like a cross section of South Korean society -- young men in factory clothes, white-collar workers with ties, a few old men and mothers with children.

At one point, demonstrators spilled off the sidewalk and blocked passage of a bus carrying journalists out of the airport. Some stuck their heads in the windows and demanded to know if Kim was aboard, then shouted their approval of him.

Later, skirmishing broke out between the demonstrators and riot police. Rocks were thrown, tear gas was fired and an unknown number of persons were arrested.

Blocks away from Kim's brick house, police formed phalanxes on sidewalks and turned away, sometimes with clubs, demonstrators who tried to march on the house.

Back in his own house for the first time since his arrest on sedition charges in 1980, Kim fended off questions about his next move against the government of President Chun.

Kim originally was sentenced to death for sedition. The sentence was then reduced to 20 years and later he was allowed to go to the United States for medical treatment.

Kim said he would consult with other opposition leaders before planning his moves. "I am not so impatient," he told reporters gathered in his living room.

In theory, any political activity by Kim is illegal.

Meanwhile, the South Korean government today issued a statement saying Kim will be free to come and go from his house to conduct his "private affairs."

That was taken to mean that police would block his way whenever they believe his purpose in going out is political.

But Kim said that after arriving home the neighborhood police commander visited him and told him not "Since when have American congressmen become like bean curd? This doesn't sound like the people who tamed the West, the pioneers." -- Choi Tae Soon South Korean spokesman to go out at all. His aides and bodyguards were told to leave, he said.

Kim said he would abide by orders not to leave his house. But his politicking seems already to have begun. Today, he said, he received a telephone call from Kim Young Sam. The two Kims, both banned, are known as the powers behind the New Korea Democratic Party, the most dynamic of three opposition parties contesting the election.

Kim arrived four days before South Koreans will elect a new National Assembly. Kim apparently hopes that the election will help his group return to prominence in South Korea politics.

Kim has maintained consistently, however, that full democratic freedoms are essential. Voting for a new assembly next week is only "window dressing," governed by an election law that is loaded against the opposition, he maintains.

Kim has also said the Chun government should open a dialogue with him and other opposition leaders and restore the civil rights of all politicians.

The Chun government condemns Kim as a man with no principles whose agitation undermines the stability necessary for economic growth and national security.