South Korea's ousted opposition leader warned today that without a peaceful transfer of power from the present government the country may face a "second student revolution" or an upheaval similar to Iran's.

Kim Young Sam, who was expelled from the National Assembly by progevernment forces last week, said sentiment is building up against President Park Chung Hee's government and suggested that time is running out.

"This government has been in power for 19 years and I don't think there's any reasonable way they could explain to the people that they need more time in power," Kim said in an interview.

He also said the United States should not support the president's "dictatorial rule," but he was not sure what U.S. oficials should do to curb it. He specifically ruled out withdrawing any of the 35,000 American troops stationed here.

(Meanwhile, Interior Minister Koo Ja Choon annouced today that South Korean police have arrested 20 members of an underground antigovernment organization loyal to Communist North Korea, Reuters reported. He said the 20 belonged to a group calling itself the Preparatory Committee of the South Korean National Libreation Front and that 54 other members were still being sought.

(The announcement came a day after a Seoul court convicted seven men on charges of spying for North Korea.)

Kim was booted out of the assembly last week by progovernment legislators for a series of critical remarks and an appeal to the Carter administration to end support for Park's "minority dicatorial regime."

Kim and most members of his New Democratic Party assert that the explusion was a vengeful act intended to remove the outspoken leader from a platform he frequently used to denounce Park.

It has produced a major political crisis in this country. The U.S. State Department expressed disapproval of the expulsion and recalled Ambasssador William Gleysteen for consultations.

Kim's followers, who include about two-thirds of the opposition party, are considering a mass resignation to protest his expulsion. Kim said today he is urging them not to resign but to press the anti-Park movement within the assembly.

A decision is expected Friday after a final party caueus.

Kim's reference today to the possibility of a "second student revolution" has a particularly potent meaning in this country. It was a student rebellion in 1960 that led to the toppling of President Syngman Rhee and to a period of instability culminating in a military coup that first put Park in office.

Late last summer, there were five large student demonstrations against the Park government in Seoul and one in a southern city, Taegu. Several persons were arrested in what amounted to the first revival of sizable student protests in nearly a year.

Kim said that another student rebellion or a revolution like Iran's could erupt unless a peaceful transfer of power is made from Park to a new government and there is an end to "repression" of dissidents.

As examples of the latest government clamp-downs, Kim cited the government's strong steps taken against his own party since last summer. Its headquarters has been raided during a workers' protest inside, editions of its newspapers have been confiscated, and its editor and Kim's chief secretary have been arrested. Government leaders have indicated Kim's critical comments could get him arrested. Any criticism of the government outside the halls of the National Assembly is prohibited in South Korea.

Now Kim's house is under constant guard.

"did you see the small police box at the end of the alley?" asked a visiting reporter. "There is a 24-hour surveillance on all movements in this house. Can that happen in a democratic country?"

Three officers occupy the police box and watch traffic moving up and down the narrow street in front of Kim's home. But his movements have not been restricted as have those of a former opposition leader and persistent critic, Kim Dae Jung.

The temporary recall of Ambassador Gleysteen reportedly startled the government, which had not anticipated so strong an American reaction. He is expected to return next week.

As he has in the past, Kim today called on the American government not to support the "dictatorial" rule in South Korea. But he emphasized that he did not have in mind any withdrawal of U.S. forces, which he said are necessary to protect the country from North Korean Communist forces.

However, he added: "I don't believe the 35,000 American troops are stationed here to protect a dictatorial rule. They are here to protect democracy in an allied nation. So I hope that the U.S. will keep on insisting on the principle of protecting decomracy."

When asked specifically what the United States should do, he replied only that is should continue offering "friendly advice" on democracy and human rights.

"It would be very difficult to say what would be adequate," he said. "I'd like to have the friendly advice from an allied nation for democracy and human rights.

"If they do advise us on these matters, it cannot be regarded as interference from a foreign nation."

Kim's previous comments published abroad had suggested that the United States should use pressure on the Park government, and he was condemned here by progovernment forces for inviting the intervention of a foreign government in Korea's internal affairs.