Karel Navarro, File, Associated Press
FILE - In this Jan. 25, 2011 file photo, Uruguay's President Jose Mujica attends a press conference at the presidential palace in Lima, Peru. Uruguay's senate is expected on Tuesday April 12, 2011 to annul an amnesty for crimes against humanity committed during the 1973-85 dictatorship. The 75-year-old Mujica, who as a Tupamaro guerrilla leader survived imprisonment during the 12-year dictatorship when more than 100 political prisoners died behind bars, was elected president with a clear majority in 2009.

MONTEVIDEO, Uruguay — Uruguay's senate debated Tuesday whether to annul an amnesty for crimes against humanity committed during the 1973-85 dictatorship, with a narrow majority expected to overrule voters who upheld the law in two referendums.

Backed by leftist President Jose Mujica, the measure would then return to the lower house for minor changes and could become law by May 20 — the day Uruguay honors the political prisoners who were kidnapped and killed during the military junta's crackdown on leftists.

Courts could then prosecute human rights violations committed in Uruguay, fulfilling a key demand of the leftist wing of the governing Broad Front coalition and complying with a 2009 Supreme Court ruling that found the amnesty unconstitutional.

Sen. Oscar Lopez Goldaracena of the Broad Front called for an end to the amnesty, saying the move was necessary for "removing the rules of impunity and granting rights to the citizenry."

Opposition parties on the right and Uruguay's retired military are angry at the change, and the issue has roiled the governing coalition as well, challenging a common political ground this small nation has built through nearly a quarter-century of democracy.

"It's clear now what kind of morality moves our enemies. It's profoundly immoral, antidemocratic," said retired Col. Jose Carlos Araujo, spokesman for the Liberty and Harmony forum of former military officials. "They don't even respect the decisions of the people."

While Argentina has made a priority of prosecuting "dirty war" crimes and Chileans are proud of the human rights prosecutions by their independent judiciary, Uruguay has largely avoided probing old wounds.

The military amnesty law — passed in 1986 as a complement to an earlier amnesty for crimes by leftists — has protected most uniformed officials ever since. The law debated Tuesday would undo the military amnesty, but leave intact the 1985 amnesty for leftist guerrillas.

A peace commission found in 2003 that 175 political opponents were eliminated during the 12-year dictatorship, including 26 in clandestine torture centers in Uruguay. But in general only crimes against humanity considered to be beyond the amnesty's scope — such as murders committed outside Uruguay — have been prosecuted, leading to prison terms for about a dozen officials.

The 75-year-old Mujica, a Tupamaro guerrilla leader who endured torture and solitary confinement during nearly 15 years in prison before he was freed due to the amnesty, was elected president with a 53 percent majority in 2009.

In that election, Uruguayans also voted by 52 percent to uphold the amnesty — only slightly narrower than the 54 percent who favored amnesty in a plebiscite 20 years earlier.

While Mujica has ruled from the center in his presidency, he seems determined to undo the amnesty and keep his promise to the most strident leftists in the Broad Front, which brings together about 20 parties and social organizations.

Mujica's predecessor, Tabare Vazquez, also now backs the change, saying: "Majorities aren't always correct in matters of human rights."

The governing coalition believes it has the necessary 16 votes with Vice President Danilo Astori acting as a tie-breaker in the 30-member senate.

The only governing coalition senator committed to backing the retention of amnesty is Jorge Saravia. His view contributed to his ouster from Mujica's Popular Participation Movement. "I respect the opinion of the people," he said.

Saravia predicted that overturning amnesty could hurt the Broad Front.

The issue is sensitive because abuses were committed on both sides. The leftist Tupamaros declared armed insurrection in 1963 against democratic governments, and their actions led to dozens of murders, kidnappings, robberies, arsons and other attacks. Vanquished by the military a decade later, they were still one of the principal arguments for the military coup in June 1973.

Uruguay's current army chief, Gen. Jorge Rosales, has said retired military members are nervous that they may be tried for murders, tortures and disappearances.

All three opposition parties — the center-right National Party, the right-wing Colorados and the Independent Party — also are against overturning the amnesty.

Colorado Sen. Ope Pasquet disputed the governing coalition's argument that Uruguayans voted in fear to uphold the amnesties. "How would they be fearful in complete democracy? To think that they voted in fear is an insult to the people."

National Party Sen. Francisco Gallinal said eliminating the amnesty "would mean a slap in the face" to the public's will.

Despite the potential for divisiveness, analysts think Uruguayans aren't likely to react by upending the middle-of-the-road politics they've built since the end of the dictatorship.

"Of course there's uneasiness. ... You can't discard the possibility of some isolated episodes," said Adolfo Garce, a political scientist at Uruguay's University of the Republic. But, he added, "An institutional breakdown cannot happen in this country."