Picture, U.S. Ambassador Lawerence A. Pezzullo, a career diplomat, has earned respect of Nicaragua's new government.UPI

"I suppose if you could peel back the roof and look down on a meeting of their government, you would hear them call us all SOBs," said one American diplomat here about U.S.-Nicaraguan relations. "And if you could listen in on us, you'd hear the same thing about them."

But when the two sides are face-to-face, he said, "things couldn't be nicer."

From Cuba to Iran, the recent history of U.S. relations with revolutionary regimes has not been a particularly happy one. Despite its own revolutionary background, the United States often has opposed radical change in other countries, especially where opposition to U.S. policies is a catalyst for revolution.

Even in those countries where the United States has tried to be friendly, new governments often prefer Washington as an enemy, using anti-Americanism as a tool for national unity. It was not until Fidel Castro accused the United States of plotting to overthrow him that the United States began seriously trying to do so.

Yet, while Washington and Nicaragua's new guerrilla government are wary, each has recognized the mutual benefits of getting along.

Four months after Sandinista National Liberation Front took power following a bloody civil war, trade is being regularized between the two countries, and a large U.S. aid program is in the works.

When U.S. Ambassador Lawrence Pezzullo invited the entire Sandinista leadership to a party for visiting American businessmen here last month, nearly all of them showed up, and stayed late. In Washington, Nicaraguan Ambassador Rafael Solis, 26, an attorney and Sandinista soldier, has just launched himself on the capital lecture circuit.

Military assistance is under discussion and what was a largely symbolic first sale -- $3,000 worth of Sandinista-requested binoculars and compasses -- was set in October. Last week, as six U.S. congressment returned home from a Nicaraguan trip, six top Sandinista commanders were touring U.S. Army bases in four states to study training techniques.

The two governments began their official relationship last July, with little reason to believe things would go smoothly.

While the Carter administration maintained it had drastically decreased traditional U.S. support for Nicaraguan dictator Anastasio Somoza, the Sandinistas measured the claim against nearly 50 years during which the United States served as the Somoza family's principal diplomatic, economic and military backer.

Although Washington ultimately pressured Somoza into resigning, its diplomats worked feverishly for nearly a year -- up until the final days before Somoza's departure -- to see installed a government more acceptable to them and prevent a popular Sandinista takeover.

The Sandinistas have made no secret of their view of the United States as an imperialist devil. Knowing of U.S. concern over Cuban influence in Latin America, they publicly thanked Castro for his support of their revolution and quickly established close ties with his country.

But during the first few weeks of Sandinista rule, much of the most potentially volatile tension dissipated, helped the the fact that neither side's worst fears were borne out. The United States did not organize an invasion of Nicaragua, or help Somoza plot to regain power. The Sandinistas did not hold mass executions of Somoza soldiers, or eliminate private property.

One reason for the smooth flow of relations, sources in Washington believe, may be that since Nicaragua was taken off the U.S. crisis list -- both because of lessening tension and Washington's distraction over other world events -- relations have been managed almost entirely by the State Department. More activist, and some say less flexible, agencies such as the National Security Council, have provided little input.

For the United States, the long-term future of its Nicaraguan ties remains uncertain. The Sandinistas are still deciding what kind of economic, political and social structures Nicaragua should have. There is rising U.S. concern, for example, over the postponed formation of a multiparty legislative council.

But "given the circumstances," the U.S. diplomat here said, "I'm amazed we're as well-off as we are."

But governments describe good personal relations between officials and a conscious attempt to go slowly and avoid thin-skinned respones to perceived provocations. At the same time, they note, Nicaragua's disastrous economic situation imposes a certain pragmatism on its politics.

Pezzullo, 53, a tough-talking career diplomat with lengthy Latin American experience, was specially chosen as ambassador last spring in hopes he could break a longstanding pattern of U.S. emissaries either coopted or intimidated by Somoza. That same toughness, however, raised initial fears here that Pezzullo would have trouble dealing with the sometimes paranoid sensibilities of the Sandinistas.

Instead, Pezzullo and most of his team appear liked and respected by the new Nicaraguan government. Pezzullo, according to officials here, has adeptly balanced awareness of the historical U.S. image with the need for firmness. He has moved out of the symbolically palatial hilltop ambassador's residence, into a smaller suburban villa.

The U.S. officials say they have found easy and frequent access to their Nicaraguan counterparts, as well as eagerness to cooperate.

While the United States currently has no official military mission in Nicaragua, Pezzullo arranged for two U.S. Army Latin specialists to be posted here temporarily from Panama.

The Sandinistas "have already informed us," one said, "that they want uniforms and . . . everything from coffee cups for the troops to sophisticated wheeled vehicles. They took us on a tour of their armored battalion, and it was enough to give an American Legion type an orgasmic heart attack -- a real collection of museum pieces, including one Italian tank Mussolini gave Somoza's father after the Ethiopian campaign."

The embassy has requested disbursement of approximately $2.5 million in authorized military assistance funds withheld from Somoza. But the Sandinistas have been cautioned that the U.S. approach to military aid here is "basically non-lethal" and that anything else "wouldn't get anywhere in the U.S. Congress."

But both sides feel their good will has been sorely tested.

Although the U.S. embassy appears to take what one diplomat called "a disconcerting level" of harsh leftist language in stride, reassured by moderation privately shown by high-level officials, there are fears that this language will cause trouble either here or in the United States.

Last September, when three members of Nicaragua's ruling junta visited President Carter on their way to the United Nations, Carter smilingly, but pointedly, told junta member Daniel Ortega he hoped Nicaragua would "be kinder" to the United States in its U.N. speech than Ortega had been three weeks before in Havana.

At the nonaligned summit conference in Cuba, Ortega had blasted American "imperialism" and came down against the United States on every issue from Cambodia to the Camp David accords.

The U.N. speech, however, varied little in foreign-policy terms, and included an added dig at those whose "investments, companies and loans" helped Somoza rob Nicaragua.

Foreign Minister Miguel D'Escoto, a Maryknoll priest who has spent most of his adult life in the United States, has become a particular thorn in the U.S. side with his public recounting of past American sins against the Nicaraguan people. Last month, he told the Organization of American States general assembly in Bolivia that the OAS should be a "Latins-only" organization without U.S. participation.

The United States is not the only supposedly friendly government that has come in for harsh criticism by what often appears a painfully insecure and somewhat disorganized government.

Several weeks ago, when Costa Rica and Nicaragua became involved in a nonpolitical OAS quarrel, a Nicaraguan embassy official in neighboring Costa Rica, whose wartime assistance was vital for the Sandinista victory, accused a highly insulted Costa Rica of "bourgeois decadence."

So far there has been no evidence of Cuban military activity here, and U.S. officials feel a strong Cuban presence in terms of teachers physicians and a number of assumed intelligence officers, is manageable.

But fear remains that identification with Cuban foreign policy, and the highly visible Cuban presence here, could become issues in a U.S. campaign year charged with emotion over the return of the Panama Canal and a perceived loss of U.S. prestige in a country where Washington once called the shots.

The Nicaraguans have their own list of grievances. When the junta met informally with the Senate Foreign Relations Committee in September, the Nicaraguans said they felt more like witnesses under criminal interrogation than visiting heads of state.

After Sen. Richard Stone (D-Fla), whose constituency includes conservative Cuban exiles, came close to accusing Ortega of lying about his past activities in Cuba, Sen. Edward Zorinsky (D-Neb.), a strong juta supporter, rushed to their defense and narrowly averted a nasty scene.

Despite U.S. promises of a postwar "mini-Marshall Plan" to help rebuild the destitute country after Somoza, substantial assistance has been slow in coming.

In congressional testimony last September, the assistant secretary of state for Latin America, Viron P. Vaky urged sympathy for Nicaragua's economic problems. For the United States to "write Nicaragua off," Vaky said, would "surely drive it to radicalization."

Yet, while a U.S. budget supplement of $120 million was drawn up by the administration in August, it was not until three weeks ago that the White House sent the Nicaragua aid request, for $75 million to Congress.

Although U.S. embassy officials in Managua pleaded that other countries were getting more mileage out of less aid rapidly distributed, the administration repeatedly withdrew the proposal for political reasons. First, it was withdrawn during the Cuba-Soviet troops crisis to append a new section for Caribbean countries, where Cuban influence was feared, and later to add another section for El Salvador, following an October coup there.