It is becoming clear that the pocket rebellion launched here by a headstrong, hard-nosed lieutenant colonel is eroding the position of Defense Minister Jose Guillermo Garcia perhaps beyond repair.
And the main hostage of the narrow feud between two of El Salvador's most powerful right-wing officers is United States policy.
The rebellion, in its fourth day Monday, is led by the Army's most effective combat commander, Lt. Col. Sigifredo Ochoa Perez, commander of northern Cabanas Province. He says he does not intend a coup d'etat against Salvadorean President Alvaro Magana.
Instead, the underlying battle is between General Garcia - an officer who has been able to work with the United States but who has proved a weak antiguerrilla commander - and Colonel Ochoa - a tough, modern warrior whose politics may be anathema to the US.
The United States is paying the price of a major involvement with an army riven with internal dissension and lack of discipline. Its largest military commitment in Central America is in El Salvador, reaching $81 million in military aid last year. Yet US Embassy personnel were apparently taken completely by surprise by the rebellion.
Colonel Ochoa has acquired an international reputation through the American press because of a pacification program he implemented in his province which almost eliminated guerrilla activity there. His military operations involve the use of small patrols and night ambushes which have been strongly advocated by US military advisers here.
General Garcia's standing with his forces fell to a low point late last year as a result of high casualties - a total of 1,040 men out of an 18,000-man Army - during a two-month guerrilla offensive that began in October and nearly paralyzed the economy for several weeks.
As recently as last week, according to a military source familiar with American thinking, the American military advisers were deeply concerned about the ''lack of a national military strategy'' in the Salvadorean Army.
However, General Garcia has enjoyed American favor as the only military man politically astute enough to bind together an unruly Army. One Salvadorean professional close to General Garcia described him as ''all the American political eggs in one basket.''
Colonel Ochoa is a right-wing nationalist who has expressed deep distrust of the American influence in El Salvador. His military training has been shaped by Israel and Taiwan. He has nevertheless managed to bind together a strange military coalition for his revolt against Garcia.
He has some sympathy from hard-line anticommunist ''warlords'', as some provincial commanders are known who feel that General Garcia has paid too much heed to United States' concerns about human rights and reform hampering them on the battlefield.
He has also developed a political friendship with the ultrarightist President of the Constituent Assembly, Roberto d'Aubuisson. They were classmates in military academy together. Mr. d'Aubuisson has made several moves since August to organize the ouster of Mr. Garcia.
Some of Colonel Ochoa's battalion officers also include men who were active in the reformist movement which carried out a 1979 coup which brought Garcia to power. Many of these officers were sent into diplomatic exile by General Garcia himself even as he maintained a public profile of support for the reforms. These officers support Colonel Ochoa's call for strict professionalism in assignments within the military hierarchy.
At time of writing Monday afternoon, the head of the Air Force and the head of one infantry brigade had withdrawn their support from General Garcia. Other key officers had taken a guarded position of neutrality. General Garcia had said he would not resign, and Colonel Ochoa says he will not resign until Garcia does.
The lack of a clear movement of support on behalf of General Garcia indicates the weakness of his position. ''It looks bad for the chief,'' said one military source who has been following the events very closely.
Colonel Ochoa does not himself want to be minister of defense. The absense of a clear, strong candidate to replace General Garcia suggests the Salvadorean Army may be facing a power vacuum for some time to come.
The rebellion has come only weeks before President Reagan must certify to Congress that progress has been made in human rights in El Salvador in order to continue military aid. Said one dismayed Embassy source, ''It's hard to organize the itinerary for visiting congressmen looking into the certification, if we don't even know what officer's name to put on the list.''