It's official: Argentina's war plans were half-baked

''Outright stupidity'' led Argentina into its disastrous war with Britain over the Falkland Islands last year. That was the assessment of one message sent the Argentine general staff in Buenos Aires from Argentine Brig. Gen. Mario Benjamin Menendez's headquarters on the Falklands during the fighting that ended with the rout of his forces in mid-June.

This message and numerous other reports contained in military archives in Buenos Aires are being looked at by the military-appointed commission probing the debacle.

None of the documents has been released as yet, but sources suggest many are bombshells that could further tarnish the Argentine military's already badly battered reputation. A military commission probing the Falklands imbroglio, meeting in secret, has already heard testimony from leading Argentine military figures, including members of the general staff and the field commanders who were in the Falklands from early April to mid-June.

It is understood that both this testimony and the archival material puts much of the blame for the Falklands debacle on the shoulders of Lt. Gen. Leopoldo Fortunato Galtieri, who had assumed the Argentine presidency in December 1981. He ordered the invasion of the islands April 2, 1982.

Now he is under house arrest for public criticism of the field commanders, including General Menendez, who commanded the ground forces in the Falklands. General Menendez has appeared before the commission but has made no public statement.

General Galtieri, on the other hand, has refused to testify before the commission, questioning its competence to handle the investigation. Since being removed from the presidency, moreover, he has made a series of public statements critical of his fellow officers. Yet many military men say he was the key figure in planning the invasion.

Before assuming the presidency in December 1981, General Galtieri is understood to have ordered the drafting of invasion plans. By Jan. 15, a month after he took office, detailed plans had been formulated. Landing sites and airstrips were pinpointed. Those airstrips that could be enlarged easily were singled out.

But it becomes clear, say those who have seen the documents, that the generals in Buenos Aires did not fully take into account their logistical preparation for war. Some munitions were in short supply; much military equipment was known to be faulty; while replacement parts and new weapons were on order, they had not yet arrived. The documents suggest that Argentina simply was not prepared for the type of war it was getting itself into.

The documents further relate a series of horror stories about military mismanagement and bungling once the struggle had begun. The battle was poorly waged, the documents suggest. It is not only General Galtieri, but also General Menendez who comes in for criticism on this score. Yet the bulk of the criticism , it is understood, rests more with the generals in Buenos Aires than the commanders on the scene.

The documents show that those who planned the invasion gave little heed to climate, terrain, and other natural conditions of the Falklands. The planners did not take into account reports on such conditions that were available in the National Library.

This library, the best single repository of material on the Falklands in Argentina, shelves more than 300 books on the islands and their environs - in Spanish, English, French, and German.

''Not one book on the Malvinas (the Argentine name for the islands) was borrowed by the military in 1981 or early 1982,'' a librarian has testified.

Moreover, three Argentine colonels who knew something about Falklands terrain , having served in military or civilian capacity on the islands during the late 1960s or '70s, were not involved in the invasion planning. Documents show that all had been dispatched out of the country on military assignments.

The point of all these reports is that while there had been some advance preparation, much was lacking - especially the sort of planning that modern armies in the NATO countries or the Communist bloc carry on.

''It is all well and good,'' wrote an unidentified Argentine Army colonel on General Menendez's staff, ''for us to know where the airfields are, to work out logistics of getting our troops to the islands, and so on, but not to know the political and cultural, historical and economic geography of the place is sheer folly.''

Other officers complained repeatedly in messages to the general staff in Buenos Aires about the need for simple items such as warm clothing and blankets. Both were in short supply. One message said poignantly:

''These are every bit as important as bullets.''