ON THE U.S.-MEXICO BORDER -- The 28-year-old Salvadoran woman, wearing old sweat clothes, tennis shoes, earrings and a black ribbon in her hair, grinned at the sight of the little fence at the bottom of the gully. She climbed through as one of her American escorts held the lightly barbed wires apart.

The woman's good cheer on a sunny day in the wooded hills of the Mexico-Arizona border region suggested a holiday outing, but she and her companions, participants in the American sanctuary movement, were breaking the law.

Government prosecutors had predicted that the movement would die after eight of its leaders were convicted last year of felony smuggling or conspiracy. But the journey of a refugee identified only as "Anna," who hiked into the United States from Mexico with sanctuary volunteers one recent morning, revealed the underground railroad still intact.

"That trial did us a lot of good," said one of Anna's escorts, an Arizona real estate broker who joined the movement in 1985 just as several leaders were arrested. "A lot of people saw that" and were repelled by the government's actions, he said.

In fact, the morning's crossing illustrated a new front that has opened in the battle between the movement and U.S. immigration officials. Besides denying political asylum to Salvadorans and Guatemalans who claim that they are fleeing persecution, the U.S. Immigration and Naturalization Service and the State Department are denying, to refugees accepted by Canada, permission to travel through the United States.

Movement leaders said Anna's husband was in a major U.S. city, with Canadian visas in hand for himself, Anna and their three children. While he waited for them, he was appealing an INS deportation order.

Canadian officials said they had some money for travel assistance to refugees cleared for arrival, but without a valid Mexican visa, Anna could not reach an airport with service to Canada. U.S. State Department officials told movement activist Jim Corbett that they could not issue a transit visa to Anna or anyone else without "a habitual place of residence" to which they could return.

"For refugees," Corbett said, "this is a classic Catch-22 situation. If they had a habitual place of residence to which they could return, they would not be refugees."

The day before movement volunteers planned to take Anna and her children across illegally, Corbett wrote the INS office in Phoenix accusing the agency of "criminal behavior in violation of basic human rights" by not carefully reading Anna's request for passage into the United States. He informed the agency that the movement would bring Anna in.

The operation involved nine people -- Americans and Mexicans -- using four vehicles to take Anna and her children across at two border points on a precise schedule.

The Americans' day began with an 85-mile drive from Tucson to the Mexican border town of Nogales, where Anna and her children had been waiting for several weeks after a difficult trip through Mexico from the Salvadoran coast. In Mexico City, she said, she had to bribe a taxi driver to keep from being forced into prostitution.

At the Nogales home where Anna had been staying, her 2-year-old daughter and 3-year-old twin sons frantically clutched at her pant legs before she left for the long, bumpy ride to the foothills. The children were too young to make the difficult hike. Sanctuary workers would bring them by car at a regular checkpoint, hoping for the usual

casual inspection of small chil- dren.

The movement has laid out so many paths into the United States that Corbett, a movement founder who was acquitted at last year's trial, said he had never used the route that brought Anna to the border. Anna's half-hour walk into the hills was uneventful, except for the roar of a farmer's truck that briefly worried her escorts. A small snake

sent her leaping straight into the

air.

Corbett, who walked with Anna to the border fence, indicated that the more difficult moments would come later, in places where U.S. Border Patrol and Drug Enforcement Administration officers often swept the rough terrain.

Anna chatted with Corbett in Spanish about his family and background and avoided piles of cattle manure on the steep paths. At the border, she was handed over to two other escorts, the real estate agent and a college student, who had hiked in from the American

side.

They would take her on what sanctuary regulars call "the Goddamned Long Run," a tortuous 90-minute trek through small canyons and up hillsides to avoid parts of the border area most easily surveyed by U.S. agents. On the way, Anna told them her story -- of neighbors in El Salvador who had been raped by government soldiers, and of her husband, who had escaped from a Salvadoran government army drafting sweep and risked prison if he returned.

By the time they reached the road where they were to rendezvous with a retired minister driving a getaway car, the temperature had climbed above 90 degrees and the real estate agent was nervous. It was Border Patrol country. "This is where the adrenalin really begins to flow," he said.

The student, on a junior year sabbatical, dashed off to look for the car. It pulled up, precisely on time, just after he left, and the real estate agent had to wait for him to return before the group could leave. The broker switched to his own car a short distance down the road and drove ahead to check the road to Tucson for Border Patrol checkpoints.

Anna seemed quieter, worrying about her children. But the minister reported that they had crossed successfully, with the border agent paying less attention to them than to a pet dog a sanctuary worker had brought along on the ride.

The student wondered out loud what that meant. "The government has been lying low," he said. "Some people think that means they have decided to treat us with benign neglect. Others say they have heard that a big bust is coming."

The movement has brought a small group of refugees across every two or three weeks in the last year, according to Corbett; 20 of the refugees were on their way to Canada. He said the movement has seen a decline in the number of political refugees as conditions in El Salvador and Guatemala appear to improve.

Harold Ezell, INS western regional commissioner, said he thinks the sanctuary movement is dead. He attributed any new activity to an attempt to raise money because of the decline in publicity since the trial. "What they ought to be doing," he said, "is helping the people who are already here to qualify for amnesty" under the 1986 Immigration Reform and Control Act. The law offers legal status to immigrants who arrived before Jan. 1, 1982.

The network of churches offering housing to undocumented Central Americans appears to be moribund. Corbett said refugees not on their way to Canada prefer to take their chances losing themselves in urban neighborhoods where other Central Americans live.

Anonymity has its uses, Corbett acknowledged, although he is so well-known he has given up cloaking his identity. He and the other escorts smiled at the sweet naivete' of Anna's suggestion, as she gleefully arrived at the border: "You ought to keep a registry of all the people who have come through, so you will know everyone you have helped."