SAN SALVADOR, July 8 (Reuters) - A Salvadoran judge on Wednesday rejected requests for parole for two of the five men convicted in the 1980 rape and murder of three American nuns in El Salvador.

Judge Gloria Platero ruled that Carlos Joaquin Contreras and Francisco Orlando Contreras must serve out their 30-year sentences, unless a higher court backs their appeals for parole.

Public defender Delmy Reyes told Reuters she had not decided whether to appeal the judge's ruling and had until Monday to do so.

Last month Platero granted parol to three other men convicted in the case: Deputy Sgt. Luis Antonio Colindres Aleman and former agents Daniel Canales and Roberto Moreno Canjura.

They have yet to be freed as government prosecutors have said they are studying whether to appeal the parole ruling.

The five men -- four former national guardsmen and their immediate superior -- were convicted in 1984 for abducting, raping and shooting to death the three nuns of the Maryknoll order and a lay worker.

The United States has said it opposes parole for the men. The killings occurred during a civil war in El Salvador during which the United States poured billions of dollars in aid into the Central American country in an effort to stop leftist guerrillas coming to power. The war, which ended with a 1992 peace pact, killed an estimated 75,000 people.