A crowd estimated at 45,000 marched to the congressional palace tonight to protest the military government's plan for a "self-amnesty" that would pardon all military personnel involved in acts of repression during Argentina's campaign against guerrillas in the 1970s.

The peaceful demonstration was the largest in Argentina since the military seized power in 1976. Police stayed at some distance from the singing, chanting marchers.

While the amnesty measure would also provide pardons to former guerrillas and other antigovernment militants who are not in hiding or abroad, it has aroused the wrath of human rights organizations, eight of which sponsored tonight's demonstration, because it would prevent a new civilian government from prosecuting police and military men accused of crimes and human rights abuses.

"There were no errors, there were no excesses, they're all assassins in the military process," sang many of the demonstrators as they marched down this capital's 9 de Julio Avenue, one of the world's widest, then turned up the historic Avenida de Mayo to the shuttered congressional palace.

The marchers stretched out for 13 blocks and included contingents representing Argentina's two major parties--the Peronists and the Radicals--and a number of leftist parties and student groups. Also in line were 1980 Nobel Peace prize winner Adolfo Perez Esquivel and retired Col. Juan Cesio, a former secretary of the Army, and numerous church leaders. Cesio, who belongs to the leftist Intransigent Party, had been arrested earlier in the day for criticizing the amnesty.

Many protesters carried placards with pictures of some of Argentina's thousands of disappeared people, while contingents of Peronist youths carried torches and beat bass drums.

The controversy over the proposed amnesty law is part of a continuing debate here over responsibility for tens of thousands of cases of torture, disappearances and deaths in the 1970s "dirty war" against leftist guerrillas and other dissidents.

International and local human rights group say that between 6,000 and 15,000 people vanished during that struggle.

The opposition to the proposed amnesty represents a broad spectrum of the social and political leadership. Argentina's conservative Catholic Church, which only months ago appeared willing to accept an amnesty as part of a process of national reconciliation, now finds itself deeply divided on the subject and said recently that the proposal was a matter of "individual conscience."

Both Peronist and Radical party presidential candidates have ridiculed the idea of a self-amnesty on the part of those accused of human rights offenses. Radical Party nominee Raul Alfonsin has taken a particularly uncompromising stand, saying that he would revoke the amnesty should he become president.

The armed forces, too, are split on both the terms and timing of the amnesty. The military high command considers an amnesty proposal that applies to both the military and its former enemy would be to hard to find unconstitutional and harder for the coming democratic government to repeal.

Gen. Cristino Nicolaides, Army chief of staff, appears to be the strongest proponent of the measure and has put his prestige on the line to get it.

Analysts here say Army nervousness over getting the amnesty approved is a reflection of the Army's failure to clean house, as the other two military services did, following the Falkland Islands war last year.

The Air Force wants to postpone the amnesty question until after the Oct. 30 presidential elections so that it can be negotiated directly with the president-elect.

The Navy has taken an agressive position against the amnesty, and news reports published here said the service would turn down the protection offered by the new law.

According to J. Iglesias Rouco, a respected columnist for the conservative Buenos Aires daily La Prensa, 90 percent of the Army's officer corps is also against an amnesty.

"The predominant opinion among officers of the three services is that there is no reason for an 'amnesty,' since individual actions that took place during the 'dirty war' were the product of orders from superiors," he said. Iglesias Rouco added that the measure also is seen as lacking political viability and deprecates the role of the armed forces in the antiguerrilla fight.