ASUNCION, Paraguay (Reuters) -- Paraguay's Senate formally began to try
                  impeached President Raul Cubas on Thursday for freeing a coup leader who is
                  his mentor and is blamed, with Cubas, for the slaying of the vice president this week.

                  A struggle for control of the Colorado Party, which has ruled Paraguay for half a
                  century, turned bloody this week with the death of Vice President Luis Maria Argana,
                  rival of Cubas and of Lino Oviedo, who is the power behind the president.

                  Congress openly blamed Cubas and Oviedo and angrily brought forward
                  impeachment proceedings scheduled for April. Cubas must defend himself
                  against five criminal charges of misuse of power which could result in him
                  being fired and even jailed.

                  In an apparent attempt to diffuse the situation, Cubas put Oviedo under
                  arrest Wednesday. Oviedo was sentenced in 1998 to 10 years in jail for an
                  attempted coup in 1996 but Cubas freed him and defied Supreme Court
                  orders to send him back to jail.

                  But the Senate went ahead anyway with the trial, reading the charges to two
                  lawyers sent by Cubas who said he had "work to do" and could not attend.

                  Unions have been staging a strike since midnight Wednesday demanding
                  Cubas' resignation over Argana's death. Thousands of supporters from both
                  factions have amassed outside Congress, separated by riot police.

                  Followers of Oviedo added to the tension by threatening violence over the
                  airwaves. "Blood will flow here," warned the pro-Oviedo radio station
                  Nanawa, calling on the former cavalry officer's followers to "garrote anyone
                  who opposes us."

                  Oviedo is a populist who has won a large following with his fiery speeches in
                  the Guarani Indian tongue of Paraguay's rural poor. He won party primaries
                  in 1998 but was disqualified from running for office by his jail sentence.

                  Cubas, his running-mate, stepped in and won the contest and Argana
                  became his deputy. But they fell out as soon as Cubas freed his friend and
                  political master in August 1998.

                  Oviedo says Argana's death in a hail of bullets Tuesday is part of a plot
                  against him and Cubas. "It's a calumny by those who want to blame me. The
                  only ones to lose out are myself and President Cubas. It's a cruel plot to
                  destabilize the president," he told the Argentine newspaper Clarin Thursday.

                  Cubas has kept Paraguay's borders closed since Tuesday to help find
                  Argana's killers. He put his brother Carlos in charge of the interior ministry
                  to lead the hunt.

                  "The police are putting all they have into investigating this barbarous murder,"
                  Carlos Cubas told Argentine radio from Asuncion. "The Paraguayan people
                  deserve better than having these killers running free in our territory."

                  Argana's killing has been condemned across the Americas, from U.S.
                  President Clinton to Paraguay's giant neighbor, and partner in the Mercosur
                  trade bloc, Brazil. Amid wild rumors of coups, self-coups and violence, the
                  Mercosur has urged Paraguay to preserve its democracy.

                  Paraguay is a pariah in Latin America, with events like Oviedo's attempted
                  coup against then President Juan Carlos Wasmosy in 1996 embarrassing its
                  reforming neighbors like Argentina and Brazil.

                  The Colorado Party has clung to power, under the corrupt dictatorship of
                  Gen. Alfredo Stroessner then, after a coup in 1989, under elected Colorado
                  governments with a reputation for corruption in a country with a huge
                  black-market economy.