None of the many problems that complicate U.S. relations with Nicaragua's Sandinista government appears to have been resolved during the 30-hour visit of the State Department's chief of Latin American affairs that ended today.

But following the departure of Assistant Secretary of State Thomas O. Enders, almost everyone here seemed a bit more relaxed. Talk of diplomatic ruptures faded. References to "hostile acts" by Washington were toned down. A joint communique, while falling short of the hopes of some Nicaraguan officials that their leaders would be invited to Washington, stipulated that Enders would return here "early in the fall" for additional discussions.

Enders held private discussions with Foreign Minister Miguel D'Escoto, the three members of the government junta and two commanders from the Sandinista Front's powerful National Directorate, as well as business, opposition and church leaders. Those familiar with the talks agree that they were blunt.

For the Nicaraguan government, there were a number of concerns. Relations with the major power in the hemisphere have been souring since at least the beginning of the year.

Among the worries for the leadership here were: cutoff of U.S. economic aid and wheat shipments to Managua early in the spring, reports of defeated members of the late dictator Anastasio Somoza's National Guard training inside the United States for an invasion, and the unexpected Senate ratification of a treaty with Colombia on July 31 that Nicaragua says infringes on its sovereignty over coastal islands.

Enders listened to all these complaints and more, according to some who met with him. But he kept returning to two central, related preoccupations of the Reagan administration.

Enders told the Nicaraguans of Washington's displeasure with what he said were sustained and possibly increased arms shipments through Nicaragua to leftist rebels in El Salvador. He also said, according to some of those with whom he spoke, that the buildup of Nicaragua's own armed forces is raising levels of hostility throughout the region.

There was no official comment on the content of the meetings from either side, but participants say the Nicaraguans denied that they were in any way supporting arms traffic to El Salvador. Regarding the phenomenal growth of their Army to at least 22,000 soldiers, with plans to reach 50,000, the Nicaraguans said such a force was necessary to defend them from possibly hostile conservative regimes to the north and even from the United States.

In one of the more brusque exchanges of the talks, said sources briefed on the meetings afterwards, Enders told the Nicaraguans that they might as well face the fact that the United States has 100 times the population of Nicaragua and in any war with Washington, Managua would come out the loser.

The Sandinistas reportedly replied that Vietnam and the Nicaragua of the 1930s, when Augusto Cesar Sandino helped force the end of a 21-year U.S. occupation, also had small populations.

Yet people familiar with the discussions said that their very bluntness helped clear the air and reduce some of the tensions leading to what D'Escoto had described as "increasingly deteriorating relations with the Reagan administration."

"This is the first opportunity we've had to talk at a high level since the advent of the Reagan administration," said D'Escoto, with whom Enders met twice during his visit. "There was an atmosphere of frankness and openness that both sides seemed to welcome."

Alfonso Robelo, a former member of the junta and now one of the most outspoken critics here of the government, had breakfast with Enders yesterday.

Robelo said later that Enders appeared to be testing the waters to see if the Sandinistas are indeed willing to develop some sort of "detente" with Washington before relations get much worse. But Robelo said that at the same time Enders was making no commitments.

"He's not giving anything. He's just putting in the thermometer," as Robelo put it.

"I think Enders is beginning to understand Nicaragua more," said a local businessman who first met the assistant secretary several months ago. "Before, he saw things very much in black and white, as if 'this is a bunch of commies we have to crush.' "

Private-sector leaders, despite the panic following Sandinista expropriation decrees July 19, said they adamantly told Enders that Nicaragua is not "lost," that a U.S. presence is important culturally and financially, and that "creative" ways must be found to maintain it. They said the aid cutoff, the wheat embargo and other moves directed by the Reagan administration against Sandinista policies hurt all Nicarguans and the last thing Washington ought to want is to give the Sandinistas a "scapegoat" for their own difficulties.