Just before midnight on Jan. 3, gunmen entered the hotel restaurant and opened fire with automatic pistols. Rodolfo Viera and Michael Hammer, who had just arrived from Washington, were killed where they sat. Mark Pearlman struggled to get away but the bullets kept coming, about 40 shots in all, and he too died.

The bullet holes in the kitchen door have been patched over and the bloodstained rug removed from the floor of the Sheraton Hotel's Las Americas restaurant. The neon light of the Copacabana roller disco flashes complacently next to the coffee shop.

But the murders, unlike tens of thousands of killings in El Salvador over the last two years, have not faded into the general background.

Two of the three men who died that evening, Hammer, 42, and Pearlman, 36, were American land reform experts working for the AFL-CIO's American Institute for Free Labor Development. Viera, 39, was head of the Salvadoran agency that oversees the controversial land distribution that the United States has made a vital facet of its policy here.

Washington, which often acts as the main international apologist for the fragile military-civilian coalition government here, has pressed Salvadoran authorities for prompt resolution of this case as well as the killing of four American churchwomen in December.

In the United States, the Catholic Church and the AFL-CIO also have pressed the investigations.

"It has often seemed to me that I was in charge of a police department instead of an embassy," acting Ambassador Frederic Chapin told Salvadoran dignitaries and the diplomatic corps as he ended his 3 1/2 months of service here Monday night. "I have necessarily been very concerned by the terrible killings of American citizens and with the cases of others who have disappeared . . . . These perfidious murders demand justice and the world will judge the government of El Salvador and its armed forces by the result of these cases."

After almost half a year of what one source called "tough slogging" between the U.S. Embassy and Salvadoran officials, suspects have been detained in both cases. Six enlisted men from the Salvadoran National Guard are being held in connection with the killing of the women and two members of wealthy Salvadoran families have been arrested for alleged involvement in the Sheraton murders.

Two military officers who were the top-ranking members of the National Guard's intelligence division were with the suspects in the Sheraton and are also being investigated, sources said.

Both majors, Maj. Mario Denis Moran and his second in command, have since been reassigned, according to these sources. Defense Minister Joe Guillermo Garcia told a reporter yesterday that while both officers were with the suspects that night, no convincing evidence has been presented against them.

Meanwhile, witnesses, investigators and some U.S. Embassy personnel involved with the cases are in almost constant danger. Consul Patricia Lasbury, herself a former nun, had the conspicuous responsibility for pressing the cases and was instrumental in shepherding some key witnesses out of the country. She has now been pulled out of El Salvador, according to friends, because of her superiors' fears for her safety.

The first prosecutor in the Sheraton case, Jorge Carlos Figeac, resigned earlier this month and left the country, alleging threats on his life. Teresa Torres Lopez, 41, a waitress who is a key witness in the Sheraton murders, is now in the United States. When she returned briefly to give a deposition, she came only as far as the heavily guarded Air Force barracks at the Ilopongo military airport.

In the Sheraton investigation, no material evidence linking the suspects to the crime has yet been made public. Ballistics tests run on the guns they say they carried that night have proved negative, sources said.

Although no one has been found who saw the actual shooting, there are some witnesses who have thus far declined to testify for the record, according to these sources. But for the moment, the only public testimony that ties the suspects to the case is in the Torres deposition.

Well-informed sources here doubt that there is even enough evidence to extradite one of the suspects from Miami, where he was arrested.

The picture given by the waitress of what happened at the Sheraton that night differs from the sworn testimony of the suspects and Maj. Moran.

According to Torres, six men were seated around one of the little tables in the coffee shop where she worked that night when Viera, Pearlman and Hammer came in. Two of the six men, she said, were Hans Christ, 31, now being held in Miami, and Ricardo Sol Meza, 34, currently in a Salvadoran jail.

Christ and Sol Meza are married to two sisters from the wealthy Aguilar family, which had thousands of acres taken by the land reform program. Sol Meza's own family controls a financial empire that includes a major interest in the Sheraton Hotel. Sol Meza himself was the proprietor of the Copacabana disco.

Torres said she could not identify the other four men at the table, but sources close to the investigation said two of them are believed to have been the majors. The names of the remaining two to whom she refers have not been revealed in the proceedings.

Viera, Hammer and Pearlman asked Torres, she said, if they could go someplace more quiet and she directed them to the restaurant Las Americas. Torres said Christ got up from his table and watched where they went.

A few minutes later, Torres said, she was taking a break on a terrace outside the restaurant when through the glass doors she saw Christ in the hallway making some sort of hand signals as if "calling people."

A volley of shots rang out seconds later. She testified that she did not see who fired them. She ran into the kitchen where she met two other hotel employes. They then entered the restaurant and saw the bodies. Sol Meza and Christ were there, according to Torres, and Christ was speaking into some kind of "apparatus." Torres said she did not see any guns.

Sol Meza subsequently told Torres and the other employes not to talk about what they saw, Torres said.

Sol Meza's story is that he never even saw the victims until after the shooting and was never in the coffee shop that night. He and Moran had dined with their wives at a Chinese restaurant then gone to visit his newly opened roller disco at the hotel, according to Sol Meza's and Moran's depositions, chatting with various friends, including Christ, that they ran into there.

It was not until someone told them something had happened in the restaurant that Sol Meza, Christ and Moran went to the scene, according to the depositions.

Sol Meza said he never said anything to anyone about keeping quiet. Nobody but Torres remembers anything about Christ speaking into an apparatus.