Border parodox: US patrols protect 'illegals'.

''It's amazing that the ones we're charged with apprehending we now have to protect,'' says Tilmon Gregg, agent in charge of the Chula Vista sector of the United States Border Patrol. ''But it's like a school of fish attracting sharks out there.''

He's talking about the thousands of Mexicans illegally crossing the border each night and the way legal responsibility and human compassion can conflict.

A special unit of Border Patrol agents and San Diego Police officers has been assigned the task of patrolling for border crime and building trust with the illegal immigrants whose instinct is to mistrust them.

Crossing at remote border points under the cover of darkness, the ''illegals'' are vulnerable targets for bandits who ply the region at night. Murder, rape, and robbery statistics for the area are high; 112 felonies have been reported so far this year. But police say statistics don't reflect the real extent of the problem because crimes aren't often reported by illegal immigrants , afraid of being sent back across the border.

''I've told aliens that if they have to cross, do it during the day,'' says Mr. Gregg. ''Working that close to the fence isn't that productive for us, so there's always going to be a no man's land where the bandits are going to be.''

In his book ''Lines and Shadows,'' Joseph Wambaugh documented in vivid, often gory detail the formation in the late 1970s of the original Border Crimes Task Force. The undercover precursor of today's uniformed patrol, that task force made headlines and heroes out of the officers who first ventured into the canyons near the border.

The unit did the tough political groundbreaking, wrote Wambaugh, on a problem that ''didn't seem to trouble very many other people. After all, they were illegal aliens, criminals by definition. But some of the criminals were only three years old, . . . and the bandits were not sentimental about mothers and babes.''

It was a modern tale of lawless banditry that officials describe much the same way today.

''In 28 years (of law enforcement work) nothing prepared me for the viciousness and brutality here,'' says Capt. Carl Ecklund. He's serious about this, and so are his officers. When they stumbled across a reporter interviewing immigrants near a popular border crossing point they were visibly angry. Ecklund later admonished the reporter, saying, ''I wouldn't go out there myself without an armed guard.''

The bandits are largely from the Mexican side, committing the crimes and conveniently running back across the border. ''The tragedy is that they're getting away with very little,'' says Ecklund, picking up a case off his desk and reading: ''$5 worth of jewelry, $10 in US cash, a pair of pants size 26.''

''Trying to convince people that we're not 'la migra' (regular immigration officers) is hard,'' says Ecklund. ''If our victims all run away, we can't do anything to build trust.''

Further complicating his problem, he says, is getting the transient immigrants to stick around for court if they agree to be witnesses in a case.

''You can't put a victim in jail,'' he says. So rapport between the police and immigrants has to be developed to ensure they'll return to help in the case.

Some see border crime as perhaps the worst, but certainly not the only, kind of exploitation that illegal immigrants find when they cross the border.