Last month Rep. Robert G. Torricelli (D-N.J.) went to El Salvador with constituent service on his mind. He wanted to learn the fate of John Sullivan, a New Jersey free-lance journalist who disappeared in December 1980.

Through the efforts of Sullivan's sister, a determined woman not put off by official indifference in Washington or El Salvador, it was learned that a body buried along a rural road might be her brother's. Last summer a body, with head and hands missing was exhumed, X-rayed and reburied. An American medical examiner compared the X-rays with ones taken of Sullivan when he was living in New Jersey. The similarities suggested that the exhumed corpse was Sullivan's.

Torricelli asked that it be released for further, and possibly conclusive, test. Promises for action were made by the Salvadoran government, but to date no officials want to assume responsibility.

All that's asked for is a body. Not an indictment of suspects. Not a trial. Not justice,, Sullivan's sister wants the smallest of comforts -- the knowledge that either her brother is dead or should be considered still missing. She'd like to pray for his soul or his return.

The Sullivan case is one of dozens of unsolved mysteries involving journalists in El Salvador. According to the Council on Hemispheric Affairs, 13 killings have occurred in the past three years. Some were Salvadorans, others foreigners. In addition to the slain, 11 other journalists are missing and presumed dead. A larger, uncounted group has been imprisoned, wounded, threatened or exiled.

Put together, the numbers represent an assault on the press that has been a war within a war. The San Salvador archdiocesan human rights office reports that last year, 5,935 noncombatants were killed; 49 by guerrillas and 5,349 by government forces and right-wing paramilitary groups. No one doubts that the same people who have been killing most of the civilians also see the press as an enemy to be eliminated.

In the current human rights certification debate, the Salvadoran government's contempt for independent journalism is seldom mentioned. The Reagan administration has an obvious interest in editing out any mention of dead, missing or jailed journalists. It has trouble enough stammering through its defense of a regime that has yet to solve the 1980 murders of the four American churchwomen. Such a question as whether government forces were responsible for the March 1982 ambush killing of four Dutch newsmen (as is suspected by independent observers) is a puzzle now all but forgotten.

Unpressured by its generous patron, the Reagan administration, the current regime refuses to make even modest concessions to fair-dealing with the press. Fifteen months ago, I was part of a three-member delegation from the Committee to Protect Journalists that went to the El Salvador embassy in Washington. We gave the ambassador a petition signed by 1,000 U.S. journalists who wanted the violence against newspeople stopped.

We asked specifically that several imprisoned Salvadoran journalists be immediately released. They had been jailed on hokey "subversion" charges. One was the 50-year-old editor of El Independiente, then the last independent paper in the country. Last week, the committee reported that the editor remains in prison, as do two others.

At the same meeting, I asked about John Sullivan. With a tone of annoyance, Ambassador Ernesto Rivas-Gallont replied that the missing reporter was "in the hills" writing a book.How did he know? Then-President Duarte told him.

That simple solutions, such as releasing a body and freeing noncriminal journalists, are too much for the regime, tells a story of judicial paralysis. More, it says that to the government and the right wing, attacking the press is as needed as killing citizens who are suspected of aiding guerrillas. Journalists are seen as aligned with the enemy. They report that the agrarian reform program is going nowhere, human rights progress is nil and U.S. military aid means more death. These are among the reasons that the guerrillas began and continue their revolution.

The absence of justice, twinned with the disappearance of a free press, means the words of the exiled Jorge Pinto, publisher of El Independiente, are as true now as when he wrote them in March 1981: "I left, not because of lack of the Salvadoran people's support for idealistic journalism, but because, after the takeover of my office and machinery, after the capture of my employes and perhaps even the eventual disappearance of my family and myself, there would be absolute silence about the facts."