A ragged line of figures moved through the shadows of the steamy night - immigration agents sweeping their flashlights through the long, low rows of bean plants looking for illegal aliens under the full moon.

"We've got some tracks here," said one agent, staring intently at a trail of footprints just a few yards from the migrant camp.

"I think," said a young woman, a slightly amused migrant from Florida, "those belong to y'all."

The agent paused for a moment. "Yeah."

The operation was not going well.

It was the first of several raids made by the U.S. Immigration and Naturalization Service along the eastern shores of Maryland and Virginia earlier this week. Working from before dawn until well after dusk, 16 agenst swept into camp after camp of the thousands of migrant workers who annually come from Texas and Florida to harvest the area's tomato, cucumber and melon crops or work in its food factories.

After 2 1/2 days, this posse of agents nabbed 51 illegal foreign migrants. In past years, they have caught twoce or three times that many. "We only scratched the surface" this year, said one exasperated officer.

The investigators from Baltimore, Washington and Norfolk cruised around the flat, sandy fields in a caravan of conspicuously antennaed cars and wire-windowed vans that set the local citizens' band radios humming with news that immigration had arrived for its annual raids.

Some agents blamed the CBs for their relative lack of success this year, but the local radios were only a minor source of their problems.

Their cars were old and temperamental: one van could rumble no faster than 50 miles an hour; a small Plymouth stalled out any time it took a fast curve. Their communications equipment had a range of less than 30 miles - forcing them to spend large chunks of their time trying to find each other when they split into different groups.

But their worst difficulties were with morale. Many of these agents feel they work for an agency that has become a legal and administrative backwater where their smallest mistakes subject them to ridicule and sometimes humiliating internal investigations.

"The problem is and has been a problem of self-image," said David Servello, acting assistant district director for Baltimore's INS office. "They have the feeling they're doing an unwanted job.... They're tired of getting kicked in the teeth."

Farmers and other employers of predominantly legal migrants complain about the agents' interference with their businesses. The foreign workers sometimes allege brutality, United States citizens sometimes get swept up in the operations and sue for false arrest.

The immigration laws themselves are a complicated amalgam of criminal and administrative rules that have had few major revisions in the last 25 years. But the environment in which they are enforced has changed radically.

"There's a new day," said Kellogg Whittick, the newly appointed INS district director for Washington and former head of the agency's enforcement division. "I don't want any [agents] riding too tall in the saddle. There was a time when you apprehended an illegal alien and he'd be at your mercy. But now they have people standing up for their rights as individuals.

"I'm not saying that we're going to coddle law violators," Whittick said. "But we must be humane."

Many of the agents in the field said these policies have resulted in reduced enforcement, despite claims to the contrary from the INS administration.

"We've got the public and the central office looking down on us," said one investigator. "We're caught in between."

As they dutifully went about their jobs this week, the agents conveyed a feeling - apparently shared by many of the migrants - that they were all involved in a futile game.

"It's kind of like cowboys and Indians," said one veteran agent. "Only these don't shoot back...usually."

The INS hit the Hurlock camp just after dark on Monday night. As soon as the cars drove up two men started running. Agents took after the two men and caught them, bringing one down with a flying tackle as he neared a stand of trees.

One said he was from Barbados. No papers. That was it. The other said, in a thick West Indian accent, that he was from West Palm Beach.

The questioning started. "You don't talk like a guy from West Palm Beach. Why were you running?"

"I was smoking marijuana," he said, sweating heavily through a T-shirt that said "Rastaman Liberation" referring to a religious cult in Jamaica. He showed a Florda driver's license.

"Anybody can buy paper [identification cards]," said an agent, training a flashlight in the man's eyes. "Let's check him with the Florida birth certificate division."

"West Palm Beach," the man repeated.

"You can come clean now or you can go to jail for a long time," said another agent.

"I was smoking pot."

"Where's your mama and daddy?"

"I don't know."

And so on. Operation supervisor Robert Daughtridge finally walked away from the interrogation.

"He might be an American, but then he might not be," Daughtridge said. "With that accent, I don't know. He may have been around these islanders so long he picked it up."

The man was left in the camp. Instead of the half dozen illegal workers they had expected they would find on the basis of a tip from the camp's owner - who said the Jamaicans were squatters he wanted removed - the agents left with only the one man from Barbados.

They hit the bit Westover migrant camp farther south in Maryland at dawn the next day. Six illegal aliens were found where, on the basis of past experience, they expected scores.

It took them the rest of the day and hundreds of miles of driving, criss-crossing the Eastern Shore, stopping in fields, at camps and poultry-processing plants, to find seven more illegal workers, including two from El Salvador and two from Thailand who first claimed to be Vietnamese refugees.

At dawn Wednesday several bleary-eyed agents arrested 16 bleary-eyed Mexicans in a camp near New Church, Va. Other Mexicans were found hiding in the rafters there, but they turned out to be legal. "We just wanted to see if you could find us," they told an investigator.

Other agents surrounded a dilapidated old house near Parksley, Va.

A migrant crew leader came out.

"We understand you've got some Mexicans in there," said Daughtridge.

"I've got a few. I wouldn't lie to you," the crew leader said. Twelve of the migrants were illegal.

But there was no running. No frantic action. No argument. The young men simply packed their bags and walked out in handcuffs with the investigators. They had come to the United States to make money, but they hadn't worked for a week, and several said they were just as glad to be going home.

They were loaded on a bus later in the day for the long ride back to the border. "You drive them down there and you say "Aya esta Mexico" and "Vaya se" [There's Mexico. Go.] and a few minutes later about half of them come back. That's the way it goes," said a senior investigator.

By breakfast time Wednesday the raids were over the agents stopped for a bite in a restaurant near New Church. They talked about their desire to go after illegal aliens who are taking high-paying jobs that Americans do want, not just stoop labor. They said they never seem to have the time to work on the cases of terrorists and drug smugglers.

A waitress came up to one of them. "Are you all down here to arrest those poor little Mexicans? They come up every year. I know some of them and they're real nice."

One investigator explained that, coming in by the millions, illegal immigrants could be a threat to the nation's resources.

The waitress laughed. CAPTION: Picture 1, Imigration agents looking for illegal aliens search a bean field during a night raid this week on an Eastern Shore migrant camp near Hurlock, Md. By John McDonnell - The Washington Post; Picture 2, Arrested Mexicans watch as others are processed. ; Picture 3, A Jamaican suspected of being an illegal immigrant is lead out of a field in handcuffs, after being picked up in Immigration and Naturalization Service raids of Eastern Shore migrant camps this week. ; Picture 4, the hands of two arrested illegal aliens are handcuffed together, one holding false papers. ; Map, By Richard Furno - The Washington Post