Former Cambodian monarch Norodom Sihanouk said today that the radical communist regime that has been driven from Phnom Penh kept him a prisoner for three years, until last week, and regularly denied Cambodians many of their human rights.

Nonetheless, Sihanouk said, he plans to begin a worldwide campaign to try to save that government.

"I did not participate in their government. I was virtually their prisoner for three years and now I must come and represent them. I am a patriot. They are patriots... They are courageous fighters, I cannot say for freedom but for national independence," Sihanouk said to 150 foreign journalists and Chinese gathered in the Great Hall of the People here.

During an extraordinary six-hour press conference while two representatives of the overthrown Pol Pot government sat in stony silence, a jovial, effervescent Sihanouk said he did not know where Pol Pot had gone after the capital, Phnom Penh, fell to Vietnamese-backed insurgents yesterday.

He lambasted Hanoi for its aggression but wondered out loud whether Cambodia's radical communists, who had asked him to undertake his campaign, still wanted him to represent them since he had exposed all their shortcomings.

Smiling, laughing and gesturing wildly, Sihanouk, 56, described in detail his life under house arrest after he returned to Cambodia from China in 1975, when Pol Pot's Communist Party took over the country. He said he lived comfortably with a garden, swimming pool, good food and books, but was prohibited from communicating with anyone but his immediate family and a few top leaders.

He bitterly denounced the Vietnamese-backed Cambodian National United Front for National Salvation as a puppet of Vietnam, the Soviet Union and the Warsaw Pact that did not have any known Cambodian leaders in it. But he added:

"If the Vietnamese allow the people to have their markets and money, and allow the Cambodians not to live in cooperatives but to have their family life, if they let the Cambodians travel to foreign countries," the people will support them.

"If the Cambodian people feel themselves happier with the Vietnamese than they were with Pol Pot, then they will not allow Pol Pot to go back and take power. Even with the finest military aid from China, we will not win," he said.

If the Chinese had a plan in letting Sihanouk speak so frankly, it might be to dissociate themselves somewhat from the defeated and in many ways unpopular radical Cambodian communists.

Although Sihanouk expressed doubt that Pol Pot would want him to continue with his diplomatic mission after making such comments, he has obtained a U.S. visa for himself, his wife Monique and two key Pol Pot foreign policy aides, Thiounn Prasith and Keat Chhonn, who sat on either side of him at today's press conference.

Officials here said the group is booked to fly to Tokyo Tuesday morning and then to New York, where Sihanouk is expected to attempt to address the United Nations on the Cambodian situation.

Sitting directly to Sihanouk's right today was Penn Nouth, who served as prime minister for his government-in-exile here from 1970 to 1975. Penn Nouth, 73, like Sihanouk a member of Cambodian royalty, shook with an old man's palsy and sat for the entire six hours without saying a word. A week ago the Pol Pot government announced that Penn Nouth had donated his ancestral wealth to aiding the fight against Vietnam.

"First of all, I must say that now I don't know exactly in what capacity I go [to the United Nations], since I don't know where my government is," Sihanouk said, laughing.

He said Keat Chhonn told him that Premier and Party Secretary Pol Pot, President Khieu Samphan, and Vice Premier Ieng Sary and "all our leaders are safe and in good shape. I don't know where they are, they could not tell me."

When asked if there was a chance the Pol Pot government would completely fold and that he would again become Cambodian leader-in-exile, Sihanouk said: "My friends here assure me the Pol Pot regime will last."

"We have the smaller part of the two parts of Cambodia," he said "They have more towns, but we have the jungles, mountains and forests."

Sihanouk praised recent American statements opposing the Vietnamese invasion of Cambodia and supporting the Pol Pot government's attempt to have a hearing in the U.N. Security Council. "President Jimmy Carter has finally decided to help the Pol Pot regime," Sihanouk said.

He said he did not know if the U.S. government "will want to meet with me or not," but that he hoped to visit New York, Washington and San Francisco as well as other parts of North America, Europe, Africa and Asia in his effort to build up opposition to the Vietnamese invasion.

"I hope the great American people will expel the Vietnamese communists from Cambodia," he said. Whenever he referred to his cooperation with the Chinese and Pol Pot from 1970 to 1975 in expelling "U.S. imperialism" from Cambodia, he apologized for having to use the term.

Sihanouk told the reporters, "I do not approve of the internal policy of Pol Pot, his violation of human rights, but his external policy is good."

Asked how he could still support a government accused of murdering thousands of its people, Sihanouk indicated he had doubts about the allegations, although he warmly complimented Voice of America corrspondent Wayne Corey on reports that included many of the Cambodian refugees' atrocity charges.

During his own few trips into the countryside, he found only happy people, Sihanouk said."Suppose there was a reign of terror. How could they laugh? How could they sing? How could they be so very gay? ...It seems that they are not terrorized. If the regime forced them to smile, we would see immediately that smile is not natural, but I know my people well and the smile was quite natural.

"The killing? What can I say about it? Marxist-Leninist visitors from other countries said, 'We did not see the killing.' I did not see the killing, so what can I tell you?"

"But I would like to see my government, the government presided over by Pol Pot, give to the people of Cambodia the right to have free practice of religion," Sihanouk said.

"I would like the government to give to people the right... to write freely. I could not write to my daughters, to my grandchildren in the cooperatives.

"I would like the people to have the right to travel very freely, not to be confined to the cooperatives, to be able to go to France for vacation, to roam freely. These are basic rights for humanity. And the right to love and be loved, the right to choose your wife and to be with your wife and children all the time, and not be separated."

He said he did not know why the Pol Pot government "chose to force upon the country such a terrible policy, but they told me genuine communism must be like this.

"I did not understand communism as a whole."

Sihanouk met with Chinese Vice Premier Teng Hsiao-ping yesterday and said he was scheduled to meet with Party Chairman and Premier Hua Kuo-feng later today.

He said the Chinese have promised support, although Peking has been publicly vague about what it will do for the Pol Pot group.

"China is studying ways to supply weapons, and even food, but it is a secret," Sihanouk said. "I do not know the secret. The Chinese know, and Pol Pot, but Sihanouk is a little man now, he is not the head of state. All I can say is that China will supply us with weapons, and all kinds of weapons, and food."

Sihanouk said Pol Pot had not asked for Chinese troops, which he said would be difficult to get into the country because the Vietnamese now controlled Cambodia's major ports and airfields, and the former major overland route, the Ho Chi Minh trail.

The former prince, whose Buddhist religion and aristocratic ways did not suit the Cambodian Communists, was asked by Pol Pot to go abroad on the dipolmatic mission only on Friday, two days before Phnom Penh fell. It was an act of desperation, for Pol Pot knew Sihanouk would make a popular advocate but also one difficult to control.

Sihanouk said the Pol Pot aides with him would try to contract Pol Pot by "radio or other means" to get further instructions for his mission.

"I will not attack Pol Pot, because he symbolizes the unity of the country. Unless he changes his national independence policy, I will speak out for Pol Pot," Sihanouk said.

Sihanouk quoted Teng as telling him Saturday, "Despite the fact that you had a somewhat unpleasant situation in Cambodia, you remain a loyal friend of your government, so Prince Sihanouk, we are ready to help you in any field."