Robert White -- the engaging, clever and, some might even say, mischievous U.S. ambassador to Paraguay -- returned here last week after a two-month home leave. A Paraguayan journalist who met the ambassador's plane at the Presidente Alfredo Stroessner International Airport asked White what he thought of the fact that, during his absence, former Nicaraguan President Anastasio Somoza had taken up residence in Asuncion.

White, who knows a leading question when he hears one and who usually cannot resist taking a well-placed poke at the more obvious deficiencies of the 25-year-old Stroessner government, broke out laughing. "Well," he said, "I think it is a bilateral problem between Paraguay and Nicaragua. It has nothing to do with the United States."

IN FACT, AS WHITE well knows, Somoza's presence in Asuncion has a lot to do with the United States. It means, for one thing, that Nicaragua's former dictator is no longer in Miami, which lets the Carter administration off the delicate political hook of having to decide whether or not to extradite him. In an odd way, unintentionally and for the wrong reasons, Stroessner has helped President Carter by giving Somoza refuge in Paraguay.

But neither Carter nor Bob White -- well-known for his outspoken stand on human rights -- is planning to return the favor. Somoza's presence in Asuncion has reinforced Stroessner's image as Latin America's last old-style dictator. This plays right into the Carter administration's game plan for Paraguay, which is to prepare the ground and maybe even hasten the day for the generalissimo's replacement by a more open, less corrupt and repressive government.

Stroessner, who came to power in 1954, is anathema to liberals and supporters of democracy in Washington and throughout Latin America. He runs a dictatorship that claims to be a democracy because Stroessner goes to the trouble of being technically reelected every five years and has his Congress pass laws that, among other things, make it a crime to "insult" the president, members of his government or the military.

This law tends to put a damper on even the most innocuous criticism. Domingo Laino, a leading democratic opponent of Stroessner's, was, for example, arrested recently and languished in jail without charges for several days, because he dared to suggest that Joao Figueiredo, the president of Brazil, had refused to meet the Paraguayan president last month. If he is charged and found guilty, Laino could be sentenced to one to six years in jail.

The law does not, however, apply to diplomats, and Ambassador White has been quite outspoken in his defense of human rights in Paraguay. Needless to say, White is not exactly Stroessner's idea of what a U.S. envoy should be.

In fact, His Excellency the President has complained that His Excellency the Ambassador is directly responsible for worsening relations between Asuncion and Washington, which is true only in the sense that White does not disguise his personal belief that human rights should be respected. White also takes obvious delight in his work, which drives Stroessner and his supporters crazy.

On his return last week, Ambassador White was asked if he had any new or special instructions from the State Department. "No," he said, "I'm just delighted to be back in Asuncion after a two-month absence.

FOR HIS PART, SOMOZA does not appear to be quite so happy to be in Asuncion after a two-month absence from Nicaragua. Those who have talked to him say he is frustrated, confused and blaming everyone and everything for his defeat -- everyone except himself.

He has publicly called President Carter "a bastard" in an interview with West German's Stern magazine and has blamed international communism, the Palestine Liberation Organization, Cuba and a week-kneed U.S. government for the Sandinista victory.

He has also told some visitors privately that he is determined to see the Sandinistas overthrown, although he said he does not think it will be possible for him to return as head of state. He has also counselled Stroessner and his ministers to hang tough and not give in to U.S. pressure for reform, according to those in a position to know.

Meanwhile, he is living in a kind of splendid isolation, occupying a huge mansion down the street from the U.S. Embassy here and leaving it only occasionally for dinner. He is not allowed to receive reporters, even those he would like to see, without the Paraguayan government's permission -- which has been infrequently granted except during the first week after Somoza arrived.

BOTH STROESSNER AND Somoza are anticommunists of the old cold-war school, which is to say that both were friends of successive U.S. administrations that automatically supported any Latin dictator who said he was against communism. But many informed Paraguayans say they think the real reason Stroessner let Somoza in was because of his money.

Asked at his sole press conference whether he planned to buy land or pursue other investment interests in Paraguay, Somoza made it clear that investing here is not what he really wants to do with his fortune.

"If the Paraguanan authorities think I have to, I will," he said, not exactly the most enthusiastic of responses.

In the meantime, Dinora Sampson, Somoza's beautiful mistress, takes care of day-to-day business while her good friend worries about their future. She also does the shopping.

When she arrived at the supermarket here recently, the owners immediately closed it so that she could be alone among the fruits and vegetables. They were not disappointed. Tacho may not be worth hundreds of millions -- as had been said and as he has denied -- but it is clear that he will never starve.

Dinora, the supermarket owners reported gleefully, spent a cool $12,000 during her trip and down the supermarket aisles.