The only remarkable aspect of Ambassador Andrew Young's speech to the Latin American economic conference in Guatemala City Tuesday was its principal author; the Rev. Dr. Brady Tyson, last seen in Geneva two months again declaring U.S. responsibility for [WORD ILLEGIBLE] the former government of Chile.

After apologizing for that historically insulatrate admission of national guilt, Tyson dropped from sight. White House aides hinted that his Geneva performance was the beginning and end of his government service. In fact, Tyson happiained the United Nations mission as [WORD ILLEGIBLE] Latin American adviser. To old hands in this region familiar with Tyson's well-established pro-Castro position, this puzzling and disturbing.

Tyson actually is quite compatible with-Young's world view. Apart from inexperience and indiscretion, the ambassador to the United Nations represents the vanguard of leftist critics of the past generation's U.S. foreign policy who are slipping under the governmental tent into the Carter administration. While overall policy from the WhiteHouse and the State Department maintains a basic anti-Communist posture, the erstwhile critics are taking over, at lower levels - particularly in Latin American affairs.

Tyson maintains associations unprecedented at a high level in the foreign-policy bureaucracy. Identified in the invitations as a State Department representative, Tyson will address a fund-raising dinner fo the Fund for New Priorities in America in New York May 19. That organization for seven years has fought the level of defense spending that President Carter now seeks to maintain.

But Tyson's past, not his present, causes all the wonderment that he is now inside the governmental tent. As a founder of the pro-Castro North American Congress on Latin America (NACLA), Tyson openly supported the hemisphere's radical left rather than democratic left - for example, Salvador Allende's Socialists in Chile rather than the Christian Democrats.

Tyson was expelled for subsversive political activity in 1966 by the rightwing government of Brazil after four years there as a Methodist missionary. Since then, on the American University faculty, he has been an activist on Latin American questions - for example, seeking to organize a 1970 student march on the Inter-American Defense College in Washington. So, when Tyson told acquaintances in 1976 that he had close contacts with candidate Jimmy Carter, the reaction was incredulity.

In naming Tyson to represent the United States at the U.N. Human Rights Commission meeting in Geneva this March, did Young know that Tyson had been expelled by our Brazilian allies? "That would recommend him to me," Young told us. After Tyson's groundless accusation of U.S. complicity in the Chilean coup, Young did not grasp the opportunity to get rid of him but placed him at the U.N. mission in New York as a political officer.

Young's speech to retired Foreign Service officers April 22 shows affinity for the line long preached by Tyson: "There has been a tremendous amount of guilt and strain on American citizens to know that for years their tax dollars have been used not to develop, not to feed the hungry, but essentially as part of an apparatus of repression in many places on the face of the earth."

Young's theme of national guilt is totally consistent with Tyson's performance at Geneva. What's more, kindred souls are quietly, without announcement, joining them in the government.

And in prospect is the transfer of economist Richard Feinberg from the Treasury to the State Department as a Latin American specialist for policy and planning. Papers found in the briefcase of Orlando Letelier, the murdered Chilean Socialist leader, list Feinberg as the prospective secret co-author of a report by NACLA, Tyson's old organization (though, in fact, Feinberg decided against through with it because of conflict with his Treasury job).

Will this transformation at low levels seep upward into policy formation? The Young-Tyson collaboration at Guatemala City has a little mild self-flagellation ("too often, it seems to me, the United States has tried to take or prempt leadership in the hemisphere") but concentrates on declarations in behalf of human rights. Left unanswered is which rights they are talking about.

A recent interview in Cuba's Bohemia magazine with Sen. George McGovern reveals how admirers of Fidel Castro define "human rights." Ridio Havana reported that McGovern praised the Cuban revolution for "guaranteeing the people fundamental human rights such as the right to eat, to work, to health, to housing and education" and "stressed that the American people need to understand that human rights are not limited to freedom of expression."

That is precisely the position taken over a decade of writing and speaking by Brady Tyson. He and less-publicized newcomers to the foreign-policy bureaucracy may soon apply a definition of "human rights" - popular in Havana but not in Buenos Aires, Santiago or Brasilia - more narrow and materialistic than Jimmy Carter ever intended.