A major battle is brewing in Congress over United States aid to El Salvador.
With the Reagan administration planning to infuse some $55 million in military equipment in El Salvador immediately, and soon to ask for a $100 -million boost in economic and military assistance for next year, congressional opponents are marshaling their arguments against increased aid.
But the administration is determined to press its view - having set its human-rights seal of approval on the Salvadoran government.
Last week it certified to Congress that the joint military-civilian junta in El Salvador had made a ''concerted'' effort to protect human rights, had achieved ''substantial control'' over security forces operating on their own, and had made progress in implementing political and economic reforms.
Not everyone agrees with this assessment.
A number of congressmen are preparing legislation to block increased aid to El Salvador, claiming that human-rights violations by the government are on the increase. Moreover, legal challenges in US courts are planned by liberal human-rights organizations.
The State Department is aware that the challenges are serious, but it obviously hopes that these difficulties can be overcome and that the legal challenges will not derail US help for the Salvadoran government.
At present, US economic aid to El Salvador is $110 million, with $25 million set aside for military assistance. The administration's aid program for fiscal 1983, now being prepared, will include at least $100 million more.
In addition, the administration announced plans Feb. 1 to pump in an additional $55 million this year, in part to replace aircraft and helicopters destroyed in a daring guerrilla raid on Ilopango Air Force Base, just outside San Salvador, last week.
''The attack, in our view and the view of the Salvadoran government,'' a State Department statement said, ''is part of a general intensification of guerrilla activity designed to sabotage the free elections scheduled for March 28.
''This is a critical juncture in Salvadoran history.''
Thomas O. Enders, assistant secretary of state for inter-American affairs, told Congress Feb. 1 that ''the decisive battle for Central America is under way in El Salvador.''
The importance of the moment is felt not only by US and Salvadoran officials but also by the guerrillas. A communique issued by one guerrilla unit said ''this is the time for us to act.''
For the Reagan administration, any delay in getting military aid to the Salvadoran Army could lead to new military losses by the Salvadoran government. Much of the additional money for fiscal 1983 would be military assistance, which administration officials regard as more critical than economic assistance.
The Salvadoran government is trying to counter stories appearing recently in the US press alleging that the Salvadoran Army has massacred hundreds of Salvadoran citizens. Salvadoran officials are seeking out representatives of the US press and other public-opinion forums to present their case in the same way that the leftist guerrillas have managed to capture attention by holding briefings, press conferences, and other sessions with newsmen.