His role is described as more that of one of Smiley's people than of James Bond -- the man who does the drudge work of international intrigue, who burns the midnight oil over superficially maeningless documents and painstakingly puts together the pieces after the G-men have given up and moved on to more adventurous pursuits.

When the Reagan administration announced, in a Feb. 23 breifing, that it had "definitive evidence" of communist aid to El Salvador's leftist guerrillas, it was Jon Glassman, a relatively unknown, 37-year-old Foreign Service officer, who stood at the State Department podium and was credited with putting the puzzle together.

It was Glassman, according to U.S. officials and diplomats in Mexico, Central America and Washington, as well as according to Glassman himself in a Mexico City interview, who discovered and pored over "18 pounds" of guerrilla documents captured by Salvadoran soliders who had blithely stacked them on an unused desk, assuming they were useless.

And it was Glassman who figured out the alleged leftist code -- that "Esmerelda," where the guerrilla chieftains had met to draw their battle plans, and "Lagos," across whose borders they were to recieve communist-promised weapons, stood for Cuba and Nicaragua.

For men like Jon Glassman, the denizens of the middle floors of a State Department where one's power is normally directly related to the position of one's office above sea-level, public recognition is rare. Even rarer is an administration that publicly produces both its intelligence analysts and the secret documents that provide grist for their analytical mills.

In recent days, the State Department has chastized the press for making too much of the Salvadoran crisis. There are U.S. officials who now refer to the entire operation -- the headlines, the high-visibility overseas missions designed to "present the evidence" to U.S. allies and the method of presentation, as a "circus."

But in the early weeks of the Reagan administration, when the perceived need to publicly "draw the line" against the Soviet Union was a high priority, the "pressure to go public" on El Salvador, according to one official, "came right from the top."

"The top," in this context, is the eighth floor office of the Secretary of State Alexander M. Haig Jr. For those in "the middle" -- few of whom dispute the authenticity of the documents or even the overall conclusions to which they point -- the origin of the pressure, the hurriedness of the plan, and the simplicity of the attack, illustrate one of the principal differences in foreign policy-making between the administrations of Ronald Reagan and Jimmy Carter.

It was last spring when Glassman first traveled to El Salvador, under orders from William G. Bowdler, then State's chief of Latin American affairs. His mission, according to U.S. officials, was to take a long look at the Salvadoran left, perphaps even to talk to them before their efforts to overthrow the U.S.-backed government there led to all-out war.

Glassman was considered the perfect man for the job. His background included a Ph.D. in Soviet studies, a stint at the U.S. Embassy in Moscow and on the State Department's Soviet desk, as well as nearly two years at the U.S. mission in Cuba. More recently, he has been assigned as political officer in the Mexico City embassy, considered a prime vantage point for Cental American rebel-watching.

Little came of Glassman's first Salvadoran trip, however.

Meanwhile, other intelligence -- much from the public record of the Commuinist Bloc and socialist press -- filtered in. Salvadoran leftist leaders gathered in Havanna during May. In June and July, Salvadoran Communist Party chief Shafik Handel visited Moscow, and Soviet leaders and Salvadoran leaders went to Managua for the anniversary of the Sandinista victory.

At the same time, the CIA and the Defense Intelligence Agency flooded Washington with informants' reports of arms shipments and alleged arms discoveries in El Salvador.

According to Robert White, the former U.S. ambassador to El Salvador, the reports were largely "unconvincing," the work of an intelligence and defense community too eager to get its fingers directly into Salvadoran territory. And the problem of piecing together what was happening in El Salvador was complicated by interagency rivalries and competing priorities.

It was not until early November -- following Reagan's election -- that the State Department felt that the "nature" of the Salvadoran conflict had changed, by virtue of intelligence intercepts, informants' reports and satellite photographs of weapons arriving in Nicaragua from Cuba and being shipped into El Salvador.

At the same time, the first large cache of alleged guerrilla documents -- including an inside account of Handel's summer trip, and the communist weapons he was promised -- was discovered. But the Carter administration's hands were tied shortly thereafter when four U.S. churchwomen were killed in El Salvador, with suspected complicity by the armed force. Until the case was solved, the State Department announced, there would be no military aid.

On Jan. 10, 10 days before Reagan's inauguration, the Salvadoran situation was brought to a climax when guerrillas launched a "final offensive" against the government. The guerrillas appeared to posses a large quantity of foreign-made arms, the administration said and, in a series of low-level official statements, it was announced that U.S. military aid to El Salvador would be renewed and increased.

On Jan. 16, four days before Reagan's inauguration, Bowdler again sent Glassman to El Salvador, one official said, "to look into foreign intervention." Other than the Handel documents, Salvadoran officials had little to offer until Glassman finding little else to do, wandered around to various security force headquarters and "found a gold mine."

In total, there were more than 80 documents: minutes of meetings within the guerrilla councils, accounts of trips to Nicaragua and statements of political philosophy and strategy. The case they made was so airtight that more than one State Department official, harking back to suspicions of an over-zealous intelligence community has referred to their discovery and contents as "a little too convenient."

For two weeks, a team of a dozen or more officials and secretaries, worked to bring together the new documents and collate them with earlier intelligence.

The report, titled "Communist Interference in El Salvador," was released Feb. 23.