By Daniela Desantis and Guido Nejamkis

ASUNCION (Reuters) - Paraguay's new president said he believes South American leaders will come to see the legitimacy of a fast impeachment trial that ousted his predecessor from office in two days and prompted criticism in the region and beyond.

Federico Franco, the former vice president, was sworn in on Friday after Congress voted overwhelmingly to remove Fernando Lugo from office, saying he had failed to fulfill his duties to maintain social harmony.

Lugo's ouster came in response to clashes over a land eviction that killed 17 police and peasant farmers a week earlier. He was a year away from completing a five-year term.

The trial's unprecedented speed raised concerns throughout the hemisphere. Leftist leaders in Argentina, Venezuela, Bolivia and Ecuador said they would not recognize the new administration and vowed to lobby for sanctions against Paraguay.

Argentine President Cristina Fernandez, who called Lugo's ouster a "coup," said measures could be adopted against Paraguay within the Mercosur trade bloc, which groups its neighbors Argentina, Brazil, Paraguay and Uruguay.

In theory, Paraguay could face suspension by Mercosur for violating the group's democratic principles. Brazil's foreign minister said leaders would discuss the situation next week at a Mercosur summit in Argentina.

"We will make contact with neighboring countries and I'm sure they will comprehend the situation in Paraguay," Franco told a news conference in the presidential palace on Saturday.

"At no time was there a rupture or a coup, there was simply a change of leadership in line with the constitution and the country's laws," said Franco, a 49-year-old doctor whose Liberal Party broke ranks with Lugo, paving the way for his removal.

Lugo decried his impeachment but said on Friday he accepted the decision of Congress and stepped down. The silver-haired former Catholic bishop has been holed up at home ever since.

Lugo has received phone calls from presidents in the region expressing their solidarity, according to his close ally, Sen. Jose Alberto Grillon.

The capital of Asuncion felt oddly normal on Saturday, with businesses opening as usual and few police officers patrolling the streets a day after they clashed briefly with protesters outside the congressional building.

Paraguay is one of South America's poorest countries and it has a long history of political instability and military rule.

The Inter-American Human Rights Commission, which is linked to the Organization of American States (OAS), voiced its concern over Lugo's impeachment.

"It's a travesty of justice and a trampling on the rule of law to remove a president in 24 hours without guarantees of due process," the commission's executive secretary Santiago Canton told reporters in Washington.

The UNASUR group of South American nations had sent a delegation of foreign ministers to Paraguay on Thursday to try to avert a quick condemnation of Lugo, arguing that he needed time to defend himself.

Ecuadorean President Rafael Correa said UNASUR could meet in the coming week to discuss Paraguay.

Paraguayan historian and political analyst Milda Rivarola, however, said she did not think Lugo would fight to be restored, appearing to accept his ouster in his final speech on Friday, and many Paraguayans felt powerless to revert the situation.

"Neighboring countries can refuse to recognize the new government, complicate negotiations or end cooperation. But I don't think they will fight for this very hard," Rivarola said, adding that the key diplomatic stance would be that of its neighbors in Mercosur, led by heavyweight Brazil.

BIG NEIGHBOR BRAZIL

Franco took care to say his new foreign minister will contact Brazilian President Dilma Rousseff, a strategic ally to Paraguay and another leftist leader in the region.

Brazilian Foreign Minister Antonio Patriota said on television in Brasilia that Brazil will not respond unilaterally and will seek regional consensus at the UNASUR meeting.

About 100,000 Brazilians live in Paraguay - a landlocked, soy-exporting nation of 6 million people - and many of them own companies, large cattle ranches or soybean farms. The two countries jointly run the giant Itaipu hydroelectric dam and Brazil is Paraguay's main trading partner.

"I don't think Brazil should apply any trade sanctions (on Paraguay). The people most affected would undoubtedly be Brazilian business executives," Franco said.

Cuba said it would not recognize Paraguay's new government. And Peru and Mexico questioned the speed of the process to remove Lugo from office. Mexico, however, recognized the legality of the impeachment process.

Germany's International Development Minister Dirk Niebel met with Franco and became the first foreign official to express support for the new government.

"I'm not a constitutional expert on Paraguay, but as a politician I think the vote in Congress sent a clear political message," Niebel told reporters in Asuncion.

(Additional reporting by Didier Cristaldo in Asuncion, Tiago Pariz in Brasilia, Omar Mariluz in Lima, Armando Tovar in Mexico City and Nelson Acosta in Havana; Writing by Hilary Burke; Editing by Anthony Boadle)