Buenos Aires — As the Anglo-Argentine conflict drags into its seventh week, a major diplomatic casualty has been Washington's relations with Argentina.
While Britain may be the honorable enemy, the United States is seen here as the unfaithful, even traitorous friend.
Argentines knew all along that there were strong US sympathies with Britain in the dispute over the Falkland Islands. But they never expected Washington to support the British cause so openly as Secretary of State Alexander M. Haig Jr. did April 30 and as President Reagan has done on numerous occasions since. There is deep resentment here over Washington's decision to abandon Argentina.
Foreign Minister Nicanor Costa Mendez puts it succinctly: ''US-Argentine relations are bad because the United States has allied itself with the enemy.''
Particularly galling to the Argentines was President Reagan's statement that the US would provide ''materiel assistance'' to the British. Sources here say there is no evidence that materiel support for the British has been given except that which has been publically known - intelligence surveillance in the South Atlantic and fuel supply for British ships at Ascension Island.
Even though no military assistance has been provided, the seeds of Argentine discontent with Washington have been planted.
Conversations with Argentine military leaders, diplomats, politicians, businessmen, labor officials, and journalists make it clear how much relations have deteriorated.
''We see Britain as an honest enemy, but our friend the United States has betrayed us,'' writes a leading Argentine journalist.
After four years of human-rights pressure from the Carter administration, Argentina was pleased with the Reagan administration's efforts to improve ties. In January, Washington was discussing resumption of suspended arms sales to Argentina. And Argentina was beginning to play a strong behind-the-scenes role in support of US policy in Central America.
There was an upbeat nature to bilateral relations. But that rekindled friendship has now been virtually extinguished.
In the 21/2 weeks since April 30, the US Embassy and US Ambassador Harry Shlaudeman have been largely shut out of high-level contacts with Argentine officials. And there has been a growing crescendo of anti-American sentiments here.
In a clear effort to curb this trend, and explore ways to repair the damage, Washington last week dispatched Gen. Vernon Walters, one of its top diplomatic trouble-shooters, to Buenos Aires.
A chief architect of closer US-Argentine ties, he has professional associations and personal friendships with a number of Argentine military leaders, including Lt. Gen. Leopoldo Fortunato Galtieri, head of the ruling military junta. General Walters' 48-hour visit here was kept secret - and not until he had left did reports of his presence leak into the press. The visit still has not been officially acknowledged by the Argentine government or the US Embassy.
Foreign Minister Costa Mendez, asked about the visit, said he knew nothing. And anyway, he added, ''I did not see General Walters.''
While here, the US trouble-shooter met largely with members of the junta - including President Galtieri, Navy Rear Adm. Jorge Issac Anaya, and Air Force Brig. Gen. Basilio Agnacio Lami Dozo.
While the visit remains hush-hush, it is understood the Argentine military leaders told General Walters that the way to restore good ties would be a Washington move away from support of Britain - and a dropping of the largely symbolic US economic sanctions imposed on Argentina April 30.
General Walters is said to have countered that Washington is Argentina's only viable leverage if it wants to get Britain to alter its Falklands Islands policy. Whether the Walter's visit did, in fact, set the stage for any restoration of the frayed ties between Argentina and the US remains to be seen. But by meeting with the Argentine junta, he certainly was able to do more than Ambassador Shlaudeman has been able to do.
Moreover, there have been a number of comments in Buenos Aires newspapers this weekend suggesting resentment of Ambassador Shlaudeman's activities, which are said to include contacts with Argentine political leaders--all of whom, the stories note, are outside the government.
Resentment over the US position on the Falklands dispute has led the US Embassy here to voluntarily dispatch some 30 nonessential personnel and their dependants. No career foreign service officers have left Argentina, however, and there are no present plans to reduce the staff further.
The size of the embassy here is not large--and hasn't been since the mid-1970 s, when leftist terrorism was rampant and embassies were often the targets of terrorist attacks. There is no US aid program, no Peace Corps operation, no military assistance program. A drug enforcement program closed its regional offices here two years ago.
In recent days the Argentine government has placed two riot-control wagons in front of the carefully manicured lawn of the sprawling US Embassy building on the edge of Palermo Chico, one of the large public parks north of downtown Buenos Aires.
Analysts here conclude that while US-Argentine relations have been battered, they have not been irreparably damaged.
But how long it takes to repair them will depend probably upon how long the current Anglo-Argentine crisis lasts - and then upon what sort of political structure is erected here in the wake of this crisis.