The general who heads El Salvador's feared National Guard has seen American "fact finders" come and go by the gross recently: 16 official and unofficial delegations in the past two weeks.

Congressmen and a television actor, doctors and a folk singer have asked about murdered nuns, tortured mothers and massacred peasants. To all of this he has provided answers about the rigorous rules and regulations followed by his men and the deceitful propaganda of communist rebels.

But when Gen. Eugenio Vides Casanova patiently denied at a dinner party Friday that he had ever tortured anyone he clearly was not ready to be called "a liar."

Other guests remember the dinner falling silent at the house of the U.S. Embassy's deputy chief of mission as Vides Casanova glared across the table at his accuser, Gino Lofredo, director of the Commission on United States-Central American Relations.

His voice rising steadily through a five-minute diatribe that dredged up American ghosts from slavery to Nagasaki to economic imperialism, the general asked rhetorically where these visitors got off telling El Salvador how to run its affairs and asking specifically if Lofredo would like to "step outside."

Lofredo demurred, and the next morning as the commission prepared to leave on schedule, some of the other members suggested that they considered the accusation against Vides Casanova "fully justified," as one put it, "but uncool."

Said an official seeing the delegation off at the airport: "You know, this was really a hard-hitting group. They made a lot of jaws drop around this town." Even a right-wing coffee grower, accosting commission member and "M*A*S*H*" star Mike Farrell at his hotel, explained in broken English, "I was very happy to see not-journalist Americans who had the guts to come down here."

The immediate motive for what some U.S. officials have called a "flying circus," even a "hootenanny" of concerned American citizens coming to El Salvador this month was the certification that President Reagan made to Congress Friday of improving human rights and reforms in this country battered by more than two years of civil war and more than half a century of bitter repression.

Most delegations represented some specific group--educators, for instance, or lawyers, or the families of the four American churchwomen allegedly murdered by national guardsmen in December 1980. They tended to make much the same rounds of the human rights groups, the military commanders, the political prisoners, the church, the embassy and perhaps some individuals of special interest to their constituencies.

But with the exception of Robert Torricelli, a freshman Democratic congressman from New Jersey who spent most of his time trying to obtain what may have been the remains of disappeared journalist John Sullivan, the son of a family in his district, the group Lofredo came with was unique in the annals of North America's burgeoning interest and moral--as well as political and military--intervention here.

A spinoff of the Center for Development Policy in Washington, funded by several liberal foundations, the commission showed an eclectic liberalism and included several writers and a businessman; former Carter administration assistant secretary of state for human rights Patricia Derian; Mary Travers, formerly of Peter, Paul and Mary; a former head of VISTA, and Farrell.

They went places other delegations have never gone and got closer to the war than most members of the U.S. Embassy are ever able or willing to do.

Rep. Edward Feighan (D-Ohio), a member of the delegation, summed up the feeling of several: "It's hard to leave here with a feeling of any security about any decision."

The group started its rounds with what even one of its own members described as a kind of "bleeding heart" predictability.

On Wednesday, Travers visited political prisoners at the Mariona penitentiary, improvising a version of "Blowing in the Wind" and "If I Had a Hammer" and talking about her trio's new song about El Salvador inspired by an article in a Roman Catholic Church magazine.

On Thursday the 18-person delegation split into three groups to look for the war in the countryside. One went out the ravaged coastal highway by the blown-up Golden Bridge to the garrison city of Usulutan. Another drove with troops into the battle-scarred heart of Morazan province.

Travers, her 23-year-old daughter, Rep. Feighan and some others, meanwhile, drove unescorted to the oft-besieged town of Suchitoto beneath the rebel bastions on the slopes of Guazapa Volcano.

A couple of hours earlier a squad of guerrillas had blasted a civilian bus with a rocket-propelled grenade because, it appeared, a few soldiers had hitched a ride on its roof. Gore was still spread on the highway as nervous troops watched the bus being pulled from a ditch.

In the town, one of the victims was laid out in a coffin in her home. Her face, half-destroyed by the blast, was covered with a handkerchief. She was 17 and had been going into the capital to register for school.

"Life here is so thankless," a young friend said again and again as children and teary-eyed old women looked to Travers for some undefined kind of help she had no idea how to give.

American-made A37B jets could be seen bombing the volcano in the distance as Travers walked to the Suchitoto hospital to see some of the survivors of the bus incident. A shot sounded near the edge of town.

"It's pretty far away," said a reporter.

Travers smiled, looking around a little warily at the bullet-pocked walls of the near-deserted city. "It's close enough for folk music," she said.

Feighan said he was up most of the night trying to resolve the conflict between what he had thought before coming here and what he had just seen.

The bus attack, he said, certainly did not show that the guerrillas murder as many people as the government appears to have done. But the burned-out bus at Kilometer 40 on the road to Suchitoto, Feighan said, "dramatized the fact that the victims in this whole situation are the peasants and they can't turn to their government and they can't turn to their self-proclaimed liberators. They are about as trapped as a people can be."

Before he came, Feighan said, he was committed to cutting off military aid to El Salvador. Now he would continue it but with the strict condition that the government here initiate and pursue negotiations with the guerrillas.

"I really think that we've been major contributors to the problem here," said Feighan, "leaving us with a major responsibility to effect a solution."

As the group left here yesterday morning, the only real consensus among them seemed to be an almost desperate desire to end the suffering and a more generalized sense that whatever is being done now by Washington is not doing the job.