United States involvement in El Salvador is inextricably linked to the small, troubled nation's record on human rights.
All possible options for US political support and economic and military aid are inevitably weighed against reports of human-rights violations.
The options President Reagan and Congress now appear to be toting up are:
* Providing El Salvador's government with increasing amounts of military and economic aid - and some US advisers. This is the Reagan administration's current strategy.
* Providing US combat personnel, an option President Reagan refuses to rule out.
* Nudging the Salvadoran government into negotiations with the left - something Mexico, France, and the Salvadoran left want, but something the United States and the Salvador government adamantly oppose.
Some observers see the US role in El Salvador as parallel to its involvement in Vietnam, especially if the US increases its number of military advisers here and then sends troops.
El Salvador's government makes it clear in public statements that it does not want US troops. US troop presence, it says, might spark dispatch of Cuban or Nicaraguan troops.
By law, the US President must certify to Congress on a regular basis that a nation qualifies for aid because it has a good human-rights record or is making progress toward one.
Thomas O. Enders, assistant secretary of state for inter-American affairs, recently made such a certification about El Salvador. He offered figures based on local Salvadoran newspapers accounts showing a reduction in the number of deaths here as proof of his assessment.
US Embassy officials here are quick to agree that these pro-government newspapers may undercount deaths, especially victims of the government's own security forces. But the embassy insists the figures coincide with other local tallies that show a downward trend in killings.
However, another analysis here shows that the downward death count referred to by Mr. Enders is downward only to the point last year at which it was reported to Congress. In the months just after that period, the trend was one of increasing deaths, this analysis shows.
The data ''shows precisely the contrary to what the Department of State is saying,'' says one source. The data is published by the Central American University here, a Jesuit institution that has been bombed many times. Some attribute the bombings to government security forces.
The university's published tally showed 9,826 civilian deaths in 1980 and 13, 229 in 1981. There was a declining number of deaths for part of 1981, but the numbers later began increasing, according to the university figures.
The university bases its figures on data gathered by the Commission on Human Rights in El Salvador and the legal aid office of the Roman Catholic Church here. In some cases the university is more conservative in its count than the rights commission and church groups, says a source. The Catholic Church here has criticized its legal aid office for not making enough effort to document the victims of the left.
A Monitor source familiar with the university tallies attributes about 30 percent of the killings to the left and the rest to the right, meaning the military and security forces. But the source, who is sympathetic to the left, called this estimation of culpability ''an educated guess.''
But the difficulty in correctly counting the number of victims in this conflict can be seen in these two cases: After a late January battle, the military claimed the left had massacred some 150 civilians. But a US Embassy team, after visiting the area, estimated some 40 civilian deaths. More recently, one of the US-based wire services sent out a story from here that cited unofficial sources as saying some 400 persons had died in a battle; the next day the military officially said the total was less than 30.
A government spokesman says the left has committed more atrocities than the right and sometimes commits atrocities to pin them on the right.
By profession, according to both the church legal aid office and the university tallies, the largest number of victims (about half) are rural peasants.
The professions of about 5,000 victims are classified as ''unknown.'' This is because the bodies were mutilated beyond recognition, the legal aid office said. Many bodies appear to have been tortured, university reports show.
In a Monitor interview, a Catholic priest here explained why a significant number of priests in the country are now committed to the cause of the left. ''The poor have a right to get organized,'' said this priest, who asked not to be identified. ''Some of the killings of the left are not justified,'' but these are far outnumbered by killings by the right, he said.
''You cannot have people oppressed during centuries,'' he said. All killing is bad, he said, but ''out of an evil you have to try to make something better.''
Breaking his public silence on the topic of human rights, US Ambassador to El Salvador Deane R. Hinton said here recently, ''Progress is being made . . . (but) violence appears once again to be rising.'' He attributed this rise to ''subversive'' efforts to sabotage the constituent assembly elections March 28, which the left is boycotting.
But Mr. Hinton also said there have been ''serious excesses'' by the Salvadoran government.
US House Speaker Thomas O'Neill says negotiations should be tried after the Salvadoran election. So far the administration has officially ruled this out, but top State Department officials met recently in the US with leaders of the left. One participant told the Monitor the US is ready to help to make contacts that might lead to negotiations.