By Daniel B. Wood | Staff writer of The Christian Science Monitor

             TIJUANA, MEXICO - In all 24 lanes of traffic stopped at the spot where Mexico meets America, idling cars stretch back toward Tijuana as
             far as the eye can see. The wait is at least an hour to reach the checkpoint and undergo inspection - a new reality of the US security
             crackdown.

             But that's a big improvement over the three hours it took to enter the US in the days and weeks immediately following Sept. 11 - except for
             one thing. As the delay here gets shorter, the number of illegal immigrants attempting to sneak into the US - inside the trunks of cars,
             strapped under seats, and even soldered inside wheel wells - is beginning to tick upward again.

             Illegal crossings here at the San Diego checkpoint, which plummeted from about 900 to 170 a week after the terrorist attacks, have not
             climbed back to pre-Sept. 11 levels. But apprehensions are unmistakably on the rise in recent weeks, an indication, perhaps, that not even
             one of the tightest border clampdowns in US history seems to be able to permanently stem illegal immigration from south of the border.

             There are a number of reasons for the increase. A temporary infusion of 20 additional Border Patrol agents - deployed here from other
             assignments after Sept. 11 - ended two weeks ago. Then, too, the holiday season is over, and more people south of the border are again
             trying to go north in search of work. Finally, in a never-ending game of "the weakest link," this checkpoint currently seems to be high on the
             list of those who trade in human smuggling.

             "They are always testing us, scoping us out, trying to overwhelm our weakest point," says William Veal, chief of the US Border Patrol's San
             Diego sector, a 66-mile swath of the border where, traditionally, more than half of all illegal immigrants gain entry to the United States.

             That's not to say the border is a wide-open sieve. In fact, it's much tighter than it was eight years ago, before the US government began
             "Operation Gatekeeper." Since then, there's been an 80 percent drop in apprehensions here (from more than 500,000 a year to about
             100,000) - an indication that fewer would-be immigrants were making the northward trek.

             Although Operation Gatekeeper has almost shut off the tide of illegal immigrants who swamped these neighborhoods for years, the migrant
             flow has spread east along the less-populated desert. It is also being funneled through the legal front door - hidden from border inspectors in
             gas tanks, under floorboards, and literally welded into dashboards.

             "Prior to 9/11, the smugglers were overwhelming us [at the checkpoint], targeting us with sheer volume," says Lauren Mack, spokeswoman
             for the San Diego sector. Her office displays photos of immigrants sewn into the upholstery of seats, or tied to engine blocks. "With the
             added attention of 9/11, we have been able to virtually shut them down," she says, "but we don't know how long that can last without
             additional manpower and technology."

             The extra 20 agents assigned here after the terror attacks helped out by wandering through the maze of waiting cars, tipping off customs
             inspectors at the booths when they saw something suspicious. But those agents have now returned to their real jobs, and the gain against
             illegal entries is slipping - still down 30 to 60 percent from the previous year, but not the 80 percent drop seen in the last months of 2001.

             Illegal immigrants and those who smuggle them are close observers of the Border Patrol's daily routine. "They know when the shifts change
             or when we have low staff, so they flood they system," says Ms. Mack. The ploy: Send in so many cars of illegals that all agents are
             deployed in their capture, or so that detainees fill the holding facility. Subsequent cars loaded with illegal immigrants simply pass the border
             unscathed.

             Smugglers chalk it up to the cost of doing business, says Adele Fasano, San Diego district director for the Immigration and Naturalization
             Service (INS), parent agency of the Border Patrol.

             The Border Patrol has some new, high-tech arrows in its quiver, however. Cameras check license-plate numbers on waiting cars, alerting
             inspectors if drivers are wanted for crimes in California or other states. Pedestrians crossing the border now must pass through metal
             detectors and have parcels X-rayed, similar to procedures at airports. Each is checked by a US agent.

             One reason the wait at the checkpoint is shorter now is a nod to complaints of trans-border students and business people, who say the
             tight security was strangling local businesses. "The very long lines make my life a hardship," says Angela Gomez, a teacher who lives in
             Tijuana but teaches across the border. She says she sometimes stands in line for two hours - each way.

             While lanes are jammed at the legal entry point, the border to the east has become increasingly difficult to pass. A ride with the Border
             Patrol tells the story: Stadium-style lights shine over a 50- to 100-yard-wide stretch of land separating two fences, now running inland for
             several miles. The first prevents vehicles from getting through. The second - a metal mesh that allows no grip - halts those trying to cross
             on foot. "Since 9/11, we've seen very little activity out here," says the Border Patrol's Ben Bauman.

             Chief Veal says the Border Patrol's long-term strategy is to copy the approach of Operation Gatekeeper: Deploy high numbers of agents to
             a target border area, then gradually reduce the number after they win control of that territory. The new emphasis, he says, is on the
             US-Canada border.

             Although no major new funding was slated for border security after Sept. 11, INS and Border Patrol officials say they're encouraged by the
             attention from Washington. Attorney General John Ashcroft recently toured the southern border, as has Rep. James Sensenbrenner (R) of
             Wisconsin, a key House committee chairman. "We are seeing the support of Congress and the administration in ways not seen before,"
             says Veal. "That is a watershed event in itself."