Debate Over INS Checkpoints Intensifies : Immigration: Fewer arrests at San Clemente, Temecula sites raise doubts on effectiveness. Officials say they remain vital.

The number of illegal immigrant arrests at two inland checkpoints north of San Diego has dropped under Operation Gatekeeper, providing fuel for those who contend that the checkpoints should be scrapped.

Some in Congress have argued that the checkpoints in San Clemente and Temecula serve no purpose and are an imposition on commuters.

However, the U.S. Border Patrol insists that they are essential to a multilayered enforcement strategy.

The Immigration and Naturalization Service has been conducting experiments to determine if the checkpoints do in fact have any effect on the level of illegal immigration. These involve closing one of the stations for a period of time and then reopening it.

The San Clemente station was closed for the first five weeks of Operation Gatekeeper, which began Oct. 1. Since reopening, arrests there were down 62% from the same period last year, the Border Patrol says. The station has 95 agents who make an average of 29 arrests a day.

At Temecula, which was open for the entire 11 weeks of Gatekeeper, apprehensions were down 52%, according to the agency. Its 75 agents averaged 23 arrests per day.

It is unclear what the figures mean long term for the checkpoints. An INS report on the issue is due this spring.

The checkpoints are controversial. Gustavo De La Vina, former chief of the San Diego Border Patrol, concedes that smugglers can easily avoid the checkpoints and that they are impractical during bad weather and on weekend evenings when traffic flows become heavy.

Unfortunately, weekend evenings are also prime time for illegal immigrants to travel.

However, De La Vina and others still believe the checkpoints are valuable for making drug seizures and as a last line of defense against illegal immigration.

Rep. Ron Packard (R-Oceanside) has pushed for closure of the checkpoints unless they are kept open 24 hours a day. Under normal conditions, they are open only at certain times.

With Operation Gatekeeper, which added new agents and equipment along the most porous section of the border separating San Diego and Tijuana, Mexico, arrests dropped 19% in the first month and 40% in the second month.