San Salvador — There has been a significant reduction in the number of political killings here in El Salvador. This downward trend is viewed by the Reagan administration as sufficient proof to support its Jan. 21 certification to Congress that El Salvador is ''making a concerted and significant effort to comply with internationally recognized human rights'' in the last six months, and is ''achieving substantial control'' over its armed forces.
But neither the dehumanized quality of the killings here in El Salvador nor the pervasive political fear among the population has changed substantially. Murders, kidnappings, disappearances, mutilations, decapitations, and numerous other forms of brutality still pervade the nation - even if at a slightly lower level than in some previous years.
And some analysts here say that the American certification process - theoretically demanding human-rights improvement as one of the key condition for continued US military aid - is waning in its force as a pressure point on the Salvadorean government. Last year El Salvador received $81 million in military aid from the United States.
In addition, some Salvadorean human-rights activists assert, the numbers of political deaths have decreased more because the civil war itself has changed than because of the effects of US pressure.
''There aren't as many unarmed people of any political tendency left to kill, '' comments one human-rights researcher sadly. He points out that as a result of the intense violence last year, many Salvadoreans have either abandoned politics or taken up arms to defend themselves. The country has become almost totally polarized.
This month's certification was President Reagan's third for El Salvador. And by now, a battery of American human-rights activists and congressmen are organized to take advantage of the forum it provides. No less than 17 congressional and other delegations came through San Salvador last week to prepare reports pegged to the certification.
According to US Ambassador Deane Hinton, over 34,000 people have been murdered in El Salvador since the beginning of the civil war in 1980.
Six different Salvadorean organizations now keep rosters of human-rights violations. Four are linked to the Roman Catholic Church, one is an information center of the Catholic University, and one the official human-rights commission of the government. They churn out rosters and charts of abuses, broken down by location, and by the age or profession of the victim.
The figures of the Catholic University, widely considered the most balanced, show that there were 11,929 deaths ''attributable to political violence'' in El Salvador in 1981. In 1982, the number was down to 4,419, or an average of 368 per month. In addition, 1,045 people were captured and remain missing.
But the bare statistics tell only part of the story. To get a clearer picture of the state of human rights here it is also necessary to look at some typical cases.
For instance, a total of 646 men and 166 women are held in two giant jails near San Salvador as political prisoners. They are awaiting trial by a secret military court established under a 1980 law, Decree 507, under which prisoners have no right to public civilian defense. During a visit last week to the men's jail, representatives of the prisoners said that none of them was arrested with any judicial order. Over half have not been told why they're being held, and none has been formally charged before a judge.
Two prisoners, Carlos Molina and Mauricio Domenech, recounted that they were captured at the same time in October, during a string of right-wing kidnappings of members of unarmed leftist opposition groups. Both say they were arrested by plainclothesmen. Both claim they were taken to a secret jail in San Salvador, where they were blindfolded and lashed to bare bedsprings for seven days of interrogation and beaten before being transferred to official custody of the National Guard.
A week after the arrests of the two men and 19 other activists and labor leaders, the armed forces confirmed publicly that they were holding the prisoners. But 13 of the political leaders arrested in October have never reappeared and are presumed dead.
''We begin to see clearly the identity of those 'heavily armed men in civilian clothes,' '' said Msgr. Arturo Rivera y Damas, El Salvador's leading Catholic prelate, in a homily late last year. ''If the authorities have a good reason to arrest a man, why do they take off their uniforms to do it?''
There are still virtually no judicial constraints on the security forces. To date, no member of any of the security forces has been convicted for a human-rights violation. As of this past December, 44 former soldiers or policeman were facing trial in civilian courts for homicide or other abuses. None has reached jury trial.
The security forces remain bound together by a passionate hatred of anyone they view as linked to communism, and by the secrets of past violence committed.
The United States has tried to pressure the Minister of Defense, Gen. Jose Guillermo Garcia, to open military trials against soldiers implicated in murder. But General Garcia has told American officials that resistance to military trial is overwhelming within the armed forces.
At the same time, in the war zone in the countryside, many officers continue to view any civilians inside areas of guerrilla influence as the enemy. This view has resulted in numerous civilian deaths in combat.