Uruguay Votes On Rights Abuses. But behind the amnesty referendum, threats of another showdown with the military

`VOTE green,'' urges one campaign, promising reconciliation. ``Vote orange,'' exhorts the other, hinting at the prospect of a military coup should the ``greens'' win. Pitted against each other in one of the hardest fought battles in Uruguay's democratic history are a citizens' group - demanding that military officers accused of human-rights abuses stand trial - and the government, defending an amnesty arrangement it made with the Army two years ago.

In a plebiscite on Sunday, citizens in favor of overturning the December 1986 amnesty law will drop a green ballot in the box. Those supporting the government's position will choose an orange slip. The latest independent polls suggest that the plebiscite could be close, but that the ``oranges'' will win.

``That should put a full stop to all discussion'' about trying Army officers on charges of torture and murder, says Vice-President Enrique Tarrigo. ``If anyone goes on talking about this issue after the vote, they will be totally isolated from society.''

Should the ``green'' vote win, Mr. Tarrigo warns, ``we will have a situation of great uncertainty.'' recalling that ``when the [amnesty] law was passed in December 1986, the country was going through moments of particular tension.''

That tension arose as the deadline approached for the appearance of military witnesses at the first trial of an Army officer for human rights abuses.

(During the period of military rule between 1973 and 1985, nearly 50,000 people - in a nation of under 3 million - are said to have passed through jail, according to the human rights group Amnesty International. The Army's rights record is one of the grimmest in Latin America.)

Army chief Gen. Hugo Medina had bluntly ordered officers not to appear in court. Rather than risk confrontation, President Julio Mar'ia Sanguinetti backed down, and congress passed a law that effectively amnestied the armed forces.

``Why should people who were prepared to disobey [the courts] in December 1986 be ready to obey them now?'' wonders Tarrigo.

``Because the government would have another sort of strength after a categorical popular vote such as the plebiscite,'' answers Matilde Rodriguez, who led the campaign to hold the referendum.

``Victory for the `green' vote is not going to generate institutional risks that could destabilize the democratic system,'' argues Mrs. Rodriguez, whose own politician husband was kidnapped and murdered in 1976.

Rodriguez's campaign, backed by a range of left-wing parties, and the Communist Party's impressive agitprop machine, has been upbeat, full of smiling suns promising a happy future ``with everyone equal under the law.''

The government has chosen a more sober approach, showing clips of the Pope with President Sanguinetti on visits to Uruguay and of European leaders praising Sanguinetti's stewardship of the transition to democracy.

The military, meanwhile, has kept its own counsel, but its opinions are not hard to guess. A recent issue of the magazine ``Soldier,'' widely read among the officer corps, argues that ``those who want to attack or put on trial members of the armed forces are doing nothing less than attacking and putting on trial the whole institution of the military.''

This was seen as a veiled threat that if the trials do restart, officers will again close ranks on the grounds that the Army itself is under fire.

Should a majority of Uruguayans decide it is not worth running the risk of such a showdown, they will vote to maintain the amnesty. Should their anger at the military run strongly enough, however, they might well decide that justice must be done. And that would present Sanguinetti with an awkward last few months in office.