From a shed beside the crude jungle airstrip, Patty Congdon radioed the "all clear" to her husband who was piloting the approaching single engine Cessna.

The passengers, an American missionary couple and their baby, were rushing for medical treatment at this base of the Wycliffe Bible Translators in southern Mexico. Missionary David Nellis had been poisoned by a treacherous jungle tree, the chechem, whose sap had badly burned and ulcerated his arms and face.

Until the Wycliffe missionaries carved this nightmarish landing strip out of the mountainside, Sochiapan's only link with the outside world was a 12-hour hike to the nearest dirt road.

Then, seven years ago, David and Christine Foris, both Wycliffe missionaries, installed a two-way radio and began to study Chinantec, the language spoken by Sochiapan's 1,300 Indians.

There are another 100 such isolated settlements in Mexico that are manned by young, mostly American, Protestant couples of the Summer Institute of Linguistics, as the Bible translators call themselves in the field. Although they have worked in Mexico since 1935, translating and spreading the Gospel among the Indians, their days here may be numbered.

After recent problems in Colombia, Peru and Brazil, the institute now is under heavy pressure from the Mexican government, which has ordered an official investigation into SIL activities. Numerous anthropologists and sociologists have demanded the immediate expulsion of the 570 institute members.

Several high officials have said openly that they consider the institute members conservative, alien teachers of the individualist ethic among Indians whose values are communitarian. The officials said they fear that SIL members are spies for the U.S. government and linked with the Central Intelligence Agency. The officials distrust SIL radio communications, airstrips, clinics and training centers. According to SIL documents, all equipment has been imported tax exempt, with official approval.

"Those Americans are the Spanish Catholic missionaries of our time. They may not see it that way, but they are the religious arm of an economic, political and cultural system," said Salomon Nahmad, director of ingenous education at the education ministry. "They're plainly part of American penetration."

Nahmad, whose ministry has jurisdiction over the institute, said the government is to blame for giving the institute "too much free reign. We really don't know what those Americans do. They know the local leaders, the political conflicts, the language. Who knows what a language is or can be used for?" said Nahmad in an interview. "We are carrying out a full investigation with lawyers, anthropologists, federal police."

The institute's current troubles in Mexico are much like those it has been having elsewhere in Latin America.

While in Peru and Brazil they recently have settled their differences with the authorities, institute members say that in Colombia and Mexico the situation is tenuous.

At the heart of the problems lies an innate suspicion on this continent of American activities - a suspicion that has grown in the last few years as activities and methods of the Central Intelligence Agency have been made public by the U.S. Congress and the pres.

When religious workers were mentioned in Congress as one of numerous CIA sources abroad, Latin American newspapers gave the news broad display.

As evidence to support such suspicion, a report here by the National College of Anthropologists cited the fact that the institute began to grow rapidly after World War II, along with U.S. power, that the institute now works in more than 25 nations and that is has received grants from the U.S. Agency for International Development.

The importance of the perception of the institute in Mexico became clear during a recent interview with a high government official who had a report on his desk prepared by Canadian sociologists. The report claimed that in Vietnam, Cambodia and Guatemala, institute members had done undercover work for the U.S. government.

"I don't know is this is true, but it's enough to make you wonder," the official said. "There is strong pressure from various quarters to throw them out."

At the sprawling compound in Tlalpan, a suburb of Mexico City and site of the institute's regional headquarters, government pressure and a press campaign have caused apprehension.

Headquarters director John Alsop had prepared reports of activities, budgets and personnel hastily and dispatched them to various government offices. The troubles, Alsop believes, are a mixture of rising nationalism, leftist attacks and lack of information "about what we really do."

""We're an American agency, and these have often been unwise and exceedingly selfish in their attitude toward Latin America," he said. "A lot of the negative reaction stems from this."

Related to the institute's problems, he believes, is Mexico's policy shift regarding its Indian minorities. For years, as foreigners flocked to the Mexican countryside to study the cultures and 58 languages of Mexico's 8 million Indians, Mexicans chose instead to study the cultures of Europe.

A significant group of anthropologists, linguists and bilingual teachers was formed by the last Mexican administration and fanned resentment of the institute.

During a recent visit to Mexico by the institute's founder, the education ministry's Nahmad remarked:

"In 40 years, you've had 300 people here with doctorates in linguistics. They have finished only 20 languages and have not helped us train one linguist.But they've produced a lot of Protestants."

In some places, the authorities have become involved in local communities' religious strife that apparently starts when fundamentalist Protestants enclunter Indians in remote jungle areas.

Indians are already cut off from the rest of society. They have their ancient beliefs, with a mix of Catholicism. Then the Protestants tell people that they are chosen and better than others in some villages. That's been disastrous," claimed a director of the government's indigenous education department.

Regardless of resentment against the Wycliffe missionaries, even critics concede that they are excellent linguists who perform tasks under difficult circumstances.

"Misunderstandings about the institute's work can be cleared up. We still have a lot of work to do in Mexico, and nobody is anxious to leave," Alsop said.

Being expelled from Mexico would be a serious setback for the institute and would affect other countries. The institute's printing shop and computer facilities in Tlalpan service m ny other Latin American countries.

At Yaxpquintehla, in the southern jungle near Guatemala, the institute has a vast training camp where all linguist-missionaries take a four-month course in jungle survival before fanning out to the 10 latin American nations where the institute works.

One possible government solution to complaints about the missionaries involves sending workers from the indigenous education department to live and work closely with each missionary couple to supervise their activities and learn their skills.

"It would be a reasonable solution," said an American anthropologist who has worked here for many years and who asked not to be identified.

"In these very isolated communities the Bible translators are often the only middlemen between the Indians and the outside world. It is perhaps not right that these middlemen should be non-Mexicans," he said. CAPTION: Picture, Roger Reeck, left, missionary from Detroit, and Mexican patients waiting in mission clinic at Sochiapan. By Marlise Simons for The Washington Post