President Carter's focus on human rights is serving to draw attention to the plight of hundreds of Mexicans held in military and civilian jails for political reasons.

A group of lawyers and a Committee of Former Political Prisoners and Relatives have begun to campaign for a presidential pardon or amnesty for 244 detainees, many of whom have spent up to six years in jail without being brought to trial.

At the same time, lawyers of the state University of Guerrero have listed the names of 257 persons who have "disappeared" in Guerrero state during the past four years as the army combed the mountains for guerrilla leader Lucio Cabanas.

The missing persons, according to the lawyers, are either held incommunicado by police or military or have died in detention.

In an apparent move to forestall a major human-rights debate, the attorney general last Monday promised to drop political charges against 76 prisoner, 46 of whom have been detained without trial since 1971.

Mexican governments routinely deny the existence of political prisoners or the use of torture. By acting as a safe haven for persecuted South American leftists and through much-repeated leftist rhetoric, recent administrations have also carved out a progressive image that has lent credibility to these denials.

In a human-rights report to the U.S. Congress covering 82 countries, the State Department said that although Mexico has a "long tradition of civic freedom," human-rights violations such as "cruel and degrading treatment are not infrequent."

Arbitrary arrests and detentions occasionally occur of political oppositionists accused of illegal activities," it added.

In recent days, five Latin American nations have rejected U.S. military aid to protest American assertions on human-rights violations. But Mexico receives no material military assistance, accepting only U.S. scholarships for military personnel.

The Mexican army, which has disbanded the country's most powerful leftist guerrilla groups, has always denied holding civilians for any length of time in its jails. Prisoners transferred last year for military to civilian jails, however, told reporters that they had seen as many as 300 detainees in Mexico City's military camp No.1

There is well-documented evidence that leftist activists - and often their relatives and friends - frequently are kidnapped by the authorities rather than arrested, are kept incommunicado, are severely tortured during interrogation and held without trial indefinitely.

During interviews, seven political prisoners said that torture by the military or by members of the Federal Security Directorate included intimidation, bestings, electric shocks, cigarette, burns and being pushed under water until near suffocation.

Five Mexico City lawyers who defend political prisoners without fee - "We're dealing with political, not legal problems," one of them explained - say there are several categories of political prisoners.

Extreme leftist guerrillas, accused of terrorist actions. There are said to be almost 100 such persons jailed.

Those charged with political crimes, such as "conspiracy" and "incitement to rebellion." The lawyers say there are close to 100 such prisoners.

Friends or relatives of the above held for questioning or as moral pressure for long periods.

Relatives of the late guerrilla leader Lucio Cabanas, for example, fall into this last category. Seven of his kin - three been held and tortured. Lucia's brother Pablo, 36, has served five years in Hermosillo jail on charges of "conspiracy." His lawyer, Guillermo Andrade, says that Pablo had no contact with his brother after 1967 and worked only as a school-teacher in a village 900 miles from where the guerilla operated. Relatives detained have charged that they were tortured.

The defense lawyers say they never receive threats from the government because they are part of what one called "our legal theater." But most of the time, they say, their representations are ignored.

"We cannot get defense witnesses to appear in court," said lawyer Carlos Fernandez del Real. "On the rare occasions when police witnesses show, they refuse to answer questions. If we need ballistic experts they are always military officers whom we cannot trust."

At a recent news conference, defense lawyers insisted that their list of 244 known political prisoners was "regrettably incomplete." In the countryside, where ploce and army can act with more impunity than in the cities, they said information is difficult to obtain.

"Peasant leaders are just locked away for trying to defend the community against abuse by authorities or people with influence," lawyer Fernandez said.

Recently the government's agency of Indian affairs published two instances of alleged abuse in its monthly bulletin charging that:

Army troops sent late last year to control "rebels" in three southern Indian villages, burned and pilfered huts and terrorized the inhabitants.

In Venustiano Carranzo in Chiapas state, 60 soldiers surrounded the village, killed two men woundedmany and took 11 prisoners.