MONTEVIDEO, Uruguay – Uruguay’s senate is expected on Tuesday to annul an amnesty for crimes against humanity committed during the 1973-85 dictatorship, overturning the view of 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 174 political prisoners who were kidnapped and killed during the military junta’s crackdown on leftists.

Courts could then prosecute human rights violations committed on Uruguayan soil, 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.

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.

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. Only exceptional crimes and murders of Uruguayans committed outside the country have been prosecuted, leading to prison terms for about a dozen officials.

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 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 some 20 parties and social organizations.

Mujica’s predecessor as president, Tabare Vazquez, who didn’t challenge the amnesty even though he had congressional majorities during his tenure, also now backs the change. “Majorities aren’t always correct in matters of human rights,” Vazquez said last month.

The governing coalition believes it has at least 16 votes in the 30-member senate in favor of overturning amnesty, including the tie-breaking vote of Vice President Danilo Astori.

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 “there’s nervousness” that now-retired military members will 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.

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.”