Argentina's military junta decreed an amnesty law today excusing all crimes committed during nine years of violent repression of terrorists, leftists and other internal opponents.

Called "a gesture of reconciliation" by the junta, the law seeks to protect the armed forces from action by a democratic government following elections Oct. 30. It exempts from prosecution dozens of top officers and hundreds of soldiers, police and paramilitary operatives who participated in torture, abductions and killings of thousands of Argentines between May 1973 and June 1982.

The amnesty law includes members of guerrilla groups who have not been legally charged until now. However, it does not cover those living abroad or those suspects who, "by their conduct have shown the intention to continue" with guerrilla organizations. The measure also excludes hundreds of suspects already sentenced to jail terms by military and civilian courts for acts of terrorism.

Common crimes, such as robbery, committed during the repression come under the amnesty, which prohibits further court investigations. It will have the effect of at least temporarily halting legal probes of Argentina's estimated 6,000 to 15,000 cases of political disappearance.

The decree was immediately condemned by every major Argentine political party and human rights group. Presidential candidates of both the Radical and Peronist parties, the electoral favorites, predicted that the law would be repealed as soon as a civilian government and congress took office.

However, several legal authorities said the law was likely to have irreversible effects, at least for those cases pending or brought before courts between now and any repeal action. The armed forces are currently scheduled to transfer power to an elected government Jan. 31.

For many in the military, which took power in a 1976 coup, the long-expected law was seen as a prerequisite for carrying out the promised withdrawal from government.

The junta also acted today on the armed forces' 1982 invasion of the Falkland Islands, the second controversial legacy of military rule. In a brief statement, the junta said it had accepted the final report of a six-member military commission established nine months ago to determine responsibility for the invasion and Argentina's subsequent military defeat by a British task force.

Informed sources said, as have widespread press reports here, that the report recommends courts-martial for at least 14 commanders, including the then president, Gen. Leopoldo Galtieri, and the two other members of the junta that launched the invasion, Adm. Jorge Anaya and Air Force Gen. Basilio Lami Dozo.

The commission also recommended action against ex-foreign minister Nicanor Costa Mendez, who led failed negotiations with Britain, and Gen. Mario Benjamin Menendez, the commander of Argentine forces in the Falklands, sources said. Navy Capt. Alfredo Astiz, notorious as an alleged participant in cases covered by the amnesty law, was recommended for court-martial by the Falklands commission for his command of Argentine forces on the island of South Georgia.

The junta offered no account of the commission's recommendations, saying only that the report would now be referred to each of the three services for study. A communique said that the junta "opportunely will issue a document to inform the public on all that was done."

While civilian leaders have long called for a public accounting by the military of the failed Falklands campaign, the commission report was all but ignored here today amid outcry over the amnesty law. For many Argentines, the military's campaign against guerrilla groups and leftists, which resulted in the disappearance of thousands of people, has become the nation's most emotional and divisive issue.

In dozens of public statements and a lengthy "final report" issued in April, armed forces leaders have maintained that the violent repression campaign was necessary to halt activities by several large and well-organized guerrilla and urban terrorist organizations that carried out hundreds of bombings and assassinations in the early 1970s.

Human rights groups and international organizations such as Amnesty International and the human rights commission of the Organization of American States have charged that military and police forces illegally abducted, imprisoned, tortured and killed thousands of suspects, including many nonviolent leftists, labor organizers and innocent bystanders. The lists of the disappeared include more than 100 journalists, a number of pregnant women and about 120 children under the age of 12.

Military leaders have admitted that "excesses" took place but have maintained they were the inevitable consequences of what they say was "a civil war."

The government also repeatedly has refused to provide a list of the disappeared or a detailed accounting of their fate. Publicly it maintains that most of those listed as disappeared are guerrillas who are in exile or undergound or who were killed in feuding between rival terrorist organizations.

For military personnel, the language of today's decree is sweeping. "The effects of this law cover authors, participants, instigators, accomplices, and those who covered up, and apply to related common crimes and related military crimes," the text says. "No one can be interrogated, investigated, called to corroborate or summoned in any way for charges or suspicions of having committed crimes or participated in the actions referred to in this law."

All ongoing investigations, it says, must be immediately dropped if they involve or appear to involve members of the police or armed forces. Civil courts have charges pending against a number of military leaders for alleged crimes, and one former junta member, retired Navy commander Emilio Massera, has been held in jail since July in a murder case.

The armed forces took more than a year to prepare the law, and its decree was delayed for months by interservice disputes over its timing and whether it should apply at all. Many officers were said to oppose the amnesty on the grounds that it implicitly acknowledged that the military had committed crimes.

Human rights groups and political leaders have campaigned against the law for months. Last month, 45,000 persons participated in an anti-amnesty march here. This week, thousands gathered for a 24-hour protest against amnesty in the Plaza de Mayo, which faces the presidential palace.

With the issuing of the law, major new demonstrations are expected in the coming days. The leaders of both the Intransigent and Christian Democratic parties called the decree an act of treason.

Augusto Comte McDonnell, a leader of the Center for Legal and Social Studies, a prestigious human rights group, said the armed forces "are trying, by means of adding one more wound to the country, to cover up their many crimes."