A new U.S. ambassador to this South American country has enraged the long-lived authoritarian government while boosting the hopes of opposition groups by taking steps to encourage an end to the dictatorial rule of President Alfredo Stroessner.

Since his arrival last November, Ambassador Clyde Taylor has made a point of meeting with opposition parties and expressing U.S. displeasure with the lack of progress toward democracy here. Paraguayan authorities have denounced Taylor for what they say is meddling in internal affairs, and local newspapers -- the major ones are controlled by relatives or friends of Stroessner -- have published editorials so critical of Taylor's behavior that some diplomats suspect the government may be thinking of declaring him persona non grata.

While Taylor has said he doubts he will be asked to leave, he is known to be concerned about the severity and personal focus of the attacks. His case illustrates the challenges confronting the Reagan administration in carrying out a revived policy of encouraging transitions to democracy in countries, including Paraguay and Chile on this continent, with entrenched authoritarian governments once supported by the United States.

Both Taylor and Harry Barnes, the new U.S. ambassador to Chile, are in delicate situations requiring them to maintain contacts with opposition groups while keeping lines of communication open to governments that have expressed no interest in talking to the opposition. Guidelines for this balancing act are set in Washington, but the ambassadors, by their account, have considerable latitude to decide what tactics to use.

Behind the U.S. shift are the lessons of Anastasio Somoza's Nicaragua and the shah's Iran, which have made the Reagan administration and its conservative backers rethink the consequences of supporting dictatorial governments that overstay whatever popular support they may have had. The U.S. worry is that such authoritarian regimes can end in social eruption that leaves political vacuums that may be filled by extremist groups.

"The message that we're trying to convey about the need for a democratic solution to societal needs here," explained Taylor in an interview, "is that only with public participation do you have a good possibility of avoiding the kind of destabilization that provides fertile ground for extremism, right or left."

U.S. officials say their aim is not to force Stroessner or Chile's Gen. Augusto Pinochet out in a way that might trigger political chaos, but rather to push for negotiated solutions and a gradual transition to democracy.

"We don't see political change here," said Taylor, a career foreign service officer who has served in El Salvador and Iran. "There's been a lot of economic and social change but not political change."

Joining the effort to find formulas for peaceful transitions has been the Roman Catholic Church, whose bishops in Paraguay and Chile have issued calls for national dialogue. Most foreign governments have also cooled relations with South America's remaining dictators, although a few countries carry on business as usual here, either out of pragmatism, as in the cases of Japan and Brazil, or out of a shared sense of international isolation, as is the case with Taiwan and South Africa.

With the cutoff of military and financial aid to Paraguay and Chile in recent years, opportunities for U.S. leverage have shrunk. But the Reagan administration still has influence as the dominant contributor to international lending institutions and moral authority as leader of the noncommunist world.

Stroessner has portrayed himself as Washington's best friend on this continent, pointing proudly to his success in keeping Paraguay free of communism. So deep is anticommunist feeling here that authorities temporarily confiscate the passports of foreign visitors if they contain visas issued by communist countries.

The arrival of the U.S. envoy coincided with the rise of antigovernment street protests. Although the main causes of the unrest are linked to domestic economic and generational factors, the government has blamed communist and outside agitators and cited Taylor as one of them.

Tensions began in early January when the U.S. ambassador visited the headquarters of the opposition Febrerista Revolutionary Party, where Taylor conferred with leaders of the National Accord, a coalition of four opposition groups that has put forward the idea of a church-mediated political dialogue with the government.

Taylor's decision to go to the signers of the accord rather than receive them at the embassy was widely interpreted as bestowing on the group a legitimacy the government had sought to deny. Interior Minister Sabino Montanaro bitterly accused Taylor of interfering in Paraguay's internal affairs, saying U.S. officials are "not entitled to legalize people whose situation is known to be irregular." He added that the only dialogue the government will accept is "the one established in the chambers [of Congress] and through elections."

Rumors circulated that the Reagan administration was financing the opposition and that the United States had given Stroessner an ultimatum to step down. Editorials charging Taylor with promoting instability and with conduct unbecoming an ambassador appeared in local papers. They reached a peak in late April when one daily, El Diario, said the U.S. ambassador had joined a demonstration called by medical workers in Asuncion to complain of low salaries.

"Since he arrived in Paraguay," said the paper, "Mr. Taylor has disregarded all acceptable diplomatic customs, adopting the attitude of a proconsul and unacceptably overstepping his duties."

After the embassy issued a statement saying Taylor was nowhere near the April 24 protest, the paper published a letter from its reporter, as well as a statement from a purported witness identified only as Elizabeth, both insisting that the ambassador was at the demonstration.

Acknowledging the danger of creating false expectations about what the Reagan administration can do to pressure Stroessner, Taylor said he has emphasized in his contacts that the United States is not trying to impose any particular political formulas.

"There's not a meeting in which I don't emphasize Paraguayan solutions to Paraguayan problems," said the ambassador, who left Asuncion last week for consultations in Washington. "In all discussions here of a political nature, we're clear that solutions to present for future Paraguayan problems must be Paraguayan."