A group of U.S. Vietnam veterans and military buffs who call themselves "adventurers" has visited here twice this year to give private military and medical training to Salvadoran troops.

The group, made up primarily of editors of Soldier of Fortune magazine, instructed Salvadorans in skills ranging from machine-gun marksmanship to water purification. Members said they accompanied Salvadorans on at least three combat patrols as observers, saying that they carried only handguns for self-defense and did not fire any rounds.

"Don't call us mercenaries," said Alexander McColl, who participated in the visits in April and August. He stressed in an interview that the group volunteered its services to the Salvadorans and that expenses were covered by the magazine.

A U.S. Embassy spokesman emphasized that the group neither sought nor received official U.S. authorization to help the Salvadoran government in its U.S.-backed battle against left-wing guerrillas. But his comments suggested that the embassy was pleased by the unofficial advisers' work because it constituted the sort of nongovernmental initiative that President Reagan frequently has lauded.

"We want to encourage private, voluntary efforts to help the Salvadorans," said embassy spokesman Donald R. Hamilton when asked about the Soldier of Fortune group.

McColl said that members of the group briefed embassy military personnel on how well Salvadoran soldiers fought in the field.

"We met with some people from milgroup the embassy's military section and told them what we knew and saw," said McColl, who was interviewed by telephone in the magazine's offices in Boulder, Colo. He is a Vietnam veteran, colonel in the Special Forces of the Army Reserve and the magazine's director of special projects.

U.S. military advisers here are barred by their superiors from traveling in combat areas and thus from judging the Salvadorans' performance first-hand. As a result, members of the magazine group said, U.S. military personnel here were happy to hear the opinions of observers with experience in the U.S. armed forces.

"Any contacts between this embassy and the Soldier of Fortune people have been informal, unofficial and at their request," spokesman Hamilton said.

Roberto D'Aubuisson, the right-wing president of El Salvador's Constituent Assembly, said last week that he would prefer retired U.S. military personnel as trainers rather than additional official U.S. advisers.

"We have enough advisers, especially considering the conditions attached to their presence," D'Aubuisson told The Associated Press.

The magazine's volunteer advisers said they were private citizens who wanted to fight international communism. The visits, however, also had many hallmarks of a magazine promotional effort.

The April trip, for instance--in which nine "adventurers" visited El Salvador for 10 days--yielded an "Expanded Central America Edition" of the magazine as its September issue. The edition included two lengthy articles describing the group's training efforts.

This month's visit--by a dozen men for about three weeks--coincided with the appearance on newsstands of the special edition. The second visit attracted American newspaper, radio and television coverage.

"We want to continue the effort to help the Salvadorans but we haven't set a schedule for any future trips," McColl said. Soldier of Fortune bills itself as a magazine for "professional adventurers" but does not specify what sort of adventure is intended.

It features articles giving first-hand accounts of current wars, reminiscences of combat in Vietnam, political analyses with a strong anticommunist slant, and technical descriptions of small arms. Its advertisements are oriented toward weapons, and its classified section includes numerous ads offering services of "experienced" mercenaries.

The visiting group was led by the editor and publisher of the magazine, Robert Brown. Members said they gave short courses in sniping, explosives and weapons maintenance. Most of the work was with El Salvador's only airborne battalion and with the elite Atlacatl Battalion, which already had received instruction from official U.S. trainers.

The group reportedly also taught Salvadorans to treat battlefield wounds. Editors of the magazine head a foundation that sent teams here in June and July to provide medical care for civilians and to train soldiers in first aid. The foundation, Refugee Relief International Inc., donated $45,000 in medical supplies to El Salvador in July, according to its president, Thomas Reisinger.

One picture in the magazine's special issue showed a smiling Salvadoran soldier draped in sashes of machine-gun bullets. The caption read, "Airborne gunner after he blew away two Gs." In the magazine's parlance, "Gs" are enemy guerrillas.

Another picture on the same page showed a Salvadoran soldier and two members of the magazine group crouching in the brush around the bodies of two dead "Gs." The picture clearly resembled photographs that hunters take after they have bagged a deer.