he two young Salvadoran recruits stood in the door of a little grocery flirting with passing girls and talking about the Cubans, Nicaraguans, Russians and Vietnamese they think they're fighting.

Everybody in the barracks here has heard the story of that dead guerrilla with the almond eyes and an earring found a few weeks ago. "Vietnamese, must have been," said one of the recruits. But no one seems actually to have seen him.

"These subversives are commanded by foreigners," the teen-age soldier nevertheless assured a visitor. "Even Russians."

Because the reports are classified it is not certain what exactly Secretary of State Alexander M. Haig Jr. was referring to when he charged at a news conference recently that foreign advisers may be assisting Salvadoran guerrillas. But there is no shortage of rumors here to fuel such speculation, plus a little bit of solid information.

Most such reports are based on guesswork.

At the National Guard headquarters here three soldiers who escaped from the town of Perquin after a guerrilla attack told a reporter they had seen a tall (by Salvadoran standards) blond man who seemed to command some of the guerrillas. They then took a closer look at the reporter. "He looked just like you," said one. "Where are you from?"

They then decided that the blond guerrilla couldn't have come from the United States. One of them said he heard the blond man speaking in a language that "wasn't English. It sounded very strange. I think it must have been Russian."

The "Russian," said the guardsmen, was carrying a camera along with his rifle. Who this man was and what he was doing in Perquin remain a mystery.

Panamanian Hugo Spadafora has talked a lot about organizing an international brigade to fight the Salvadoran government like the group he organized two years ago to fight in Nicaragua's civil war, but such a group has never been reported in action in El Salvador.

In more than a year of sporadic fighting and claims that massive aid is being sent the guerrillas by the Soviet Union and its allies, only one alleged foreign adviser has ever been captured by the government.

He was an 18-year-old Nicaraguan named Tardencillac Espinoza Por, who appeared at several news conferences put on by the Salvadoran military in February and March and claimed that he had commanded a group of about 180 guerrillas in southern El Salvador during the January offensive.

He said he was in the Nicaraguan Sandinista Army when he was selected for the mission, and he arrived to train partisans at the Salvadoran national university in 1980.

But most reported "foreign advisers," like the "Vietnamese," are found dead, without papers, and identified by the military on the basis of skin color judged too dark or too pale to be Salvadoran. Other reports are based, like that about the "Russian," on hearing some strange accent, even Spanish that seemed--to the listener in the middle of a firefight--filled with Nicaraguan or Cuban phonemes.

The extent to which soldiers hear what they want to hear and see what they want to see is impossible to establish. But these two recruits in front of the grocery are absolutely sure that when they finally get into combat they will be up against foreign commanders. "We're going to be fighting the Russians," one assured a reporter. "Russians," agreed his buddy.