Prince Norodom Sihanouk, exiled ruler of Cambodia, gave a party last night at the Hay-Adams Hotel for most everyone he knew or who knew him in Washington. Like a dutiful host, he greeted guests in one of three languages (English, French or Khmer) and directed them to two buffet tables laden with food.

And then he sang for them.

Taking the microphone cheerfully as Cambodian musicians sang backup, Sihanouk convincingly crooned French ballads, then popular Cambodian songs.

He smiled contentedly at his dancing guests. And he kept singing, donning glasses to read music that he set up on a stand. "He's a great host," said Robert Moore, the deputy chief of the U.S. mission in Cambodia from 1959 to 1962. "Very attentive to the interests of his guests."

Guests came and went, refilled their glasses, chatted with friends. Sihanouk kept singing. How long would he sing?

"Until midnight," said one Cambodian, when midnight was still two hours away. "Until 2 a.m.," said another nonchalantly.

"I heard of a party he gave in New York," said Moore. "Everyone was so happy to see him. He stayed until 4 a.m."

Sihanouk had gathered a crowd last night that one guest called "his court in exile." Hundreds came -- Americans who had known him in various decades in power and then out, Cambodians from those years, and Cambodian refugees who live here now.

The refugees turned out in large numbers. Polite in a way rarely seen at Washington parties -- where a guest's physical location can determine whether the evening is a loss or success -- they hung back from the dance floor when it was crowded. They stood in courteous near-silence in two lines close to one buffet table, never pushing their way through to Sihanouk, but instead forming a natural flank for those officials of the corps diplomatique, as Sihanouk called them, who strode up to greet the prince.

"It's very crowded, I apologize," Sihanouk said breathlessly, bowing, hands together, in greeting to one couple. "I beg you, I beg you . . ." he said, pointing to a buffet table.

"Vous excusez!" he cried to another couple in similar apology.

"Please! Please!" he exclaimed to one Chinese minister as he escorted him to the buffet.

Sihanouk's country was once an Asian paradise, but the Vietnam war and the brutal four-year rule of the Khmer Rouge have transformed it into a Southeast Asian tragedy. One to three million Cambodians died during that rule. It ended when the Vietnamese invaded Cambodia in December 1978.

Now, Sihanouk -- the man Cambodians considered semi-divine and before whom they genuflect -- has allied himself with the Khmer Rouge and another resistance faction. Approved by the United States and allowed to represent Cambodia at the United Nations, the alliance has vowed to throw out the Vietnamese. Without the alliance, Sihanouk -- who serves as its president -- would have no official voice. But how do the Cambodians feel about this alliance?

"They understand quite well!" he exclaims, arms shooting out. "We have to have the alliance to get international recognition!" His voice booms, his face is pained. He is a small man with graying hair, immaculate in a black three-piece suit, white shirt and gold silk tie. "If I form a government without the Khmer Rouge, how can I represent my people?" His face crinkles up as if he is about to cry.

"Nobody would listen to me -- if I'm not the president of my country." His arms are outstretched and he leans back. He looks as if any second, his eyes will shed tears. Then he launches into more argument.

Sihanouk and the coalition's prime minister, Son Sann, breakfasted with Vice President George Bush last week before spending some time in New York. "It was a very nice, very friendly meeting," Sihanouk said. "The U.S. supports us in our efforts to regain independence for Cambodia."

Indeed, the display of State Department officials last night was evidence enough of that. The United States has said, however, that it will give no military support to the rebels battling the Vietnamese in Cambodia. Sihanouk, who lives in Peking, came back to Washington yesterday to give a reception for his friends here. The Chinese--no friend of the Vietnamese in Cambodia--paid for Sihanouk's trips.

"Because I'm poor!" cried Sihanouk. "And our people cannot pay taxes."

"He'll be 60 on Oct. 31," said Kiri Tith, a faculty member at the Johns Hopkins School for Advanced International Studies, whose father was one of Sihanouk's prime ministers during his 29-year rule. "He meant to have a party in Peking but he couldn't make it there. He has to stay here longer. So he's having it in Paris." Tith chuckled. "He said he's a refugee like everyone else. No home."