San Ysidro, Calif. — The rosy glow of a Pacific sunset signals the end of the day in the San Diego metropolitan area. But here, high above the city and ocean, the San Ysidro hills come to life at dusk.
Where the hills dip to the Mexican border, several hundred Mexicans milled about on a recent evening. Eyeing US Border Patrol agents to the north and the setting sun to the west, they waited for darkness to cloak their scurry across the border.
An island of rugged terrain dividing the urban seas of Tijuana and San Diego, the hills and maze-like canyons of San Ysidro are striped with the well-worn footpaths of Mexicans traveling north into the United States. Hundreds of Mexicans - 1,000 on a recent evening - are apprehended every night by the Border Patrol here in the most heavily trafficked sector of the 2,000-mile US-Mexican border.
From the vantage of these hills the political and economic controversy over the ''flood of illegal aliens'' takes on very tangible dimensions.
The nightly lineup at the border appears to be a testament to year-end statistics showing record numbers of aliens caught during the holiday season - traditionally the slowest period in the migration cycle.
There were 20 percent more recorded apprehensions in the San Diego area during the last three months of 1982 over the same period in 1981, reports Dale Musegades, deputy chief of the Chula Vista Border Patrol sector (which includes the whole San Diego area). December is traditionally the slowest month of the year, with roughly one-third of the number caught during peak months. But during December 1982, nearly 20,000 apprehensions were made - much more than half the 33,500 peak in March.
While December had the year's lowest number of captures, its relative position ''. . . more than likely represents a real increase in apprehensions,'' says Dr. Wayne Cornelius, director of the Center of US-Mexican Studies at the University of California, San Diego.
Critics of the Border Patrol say these statistics aren't a fair gauge of the number of aliens crossing the border because of multiple apprehensions of individuals and the absence of crosschecks on each apprehension. But Dr. Cornelius says the numbers provide a ''rough proxy'' of the intensity of pressure to cross the border.
The sustained alien influx at San Diego is the most dramatic of any border area. But El Paso, Texas, officials say they've seen an interesting twist in the statistics. Record cold and snow in the El Paso area was expected to decrease the flow of aliens by 4-5 percent. Instead, there was a 7 percent increase in apprehensions over December 1981.
With the Mexican economy still floundering and the record influx of aliens during the holidays, Border Patrol officials say they wonder what increases they'll face during the normal peak period of March and April.
Reintroduction and passage of the Simpson-Mazzoli bill in Congress will put more teeth in immigration laws, says Border Patrol agent Aaron Billings. Meanwhile, he says, one attempt to upgrade enforcement begins this week with a month-long blitz that will import 40 extra agents to man several new infrared night scopes.
A casual visual inspection of the border situation here in San Ysidro confirms that the mere concept of an international border and a handful of agents to police it is no barrier to the economic incentives the US dangles before a nation saddled with 50 percent unemployment and 100 percent inflation.
One 21-year-old Mexican lay silent in a celery field just beyond the hills until Agent Billings nearly tripped over him while flushing out other aliens. The young man offered a typical example of why the Mexicans come to the US. He said he left a job with an electric company in Durango, Mexico, to get a better-paying job in Los Angeles. Asked how much he was paid in Durango, he said , ''1,800 pesos'' - about $12 - a week. The US may be struggling with its own economic problems. But compared with Mexico, it is still the ''land of opportunity,'' explains Leonor Ramirez, executive director of Centro de Asuntos Migratorios, a San Diego social service organization. Despite high US unemployment, she says, ''There are plenty of jobs . . . the jobs a US citizen will normally not take'' that Mexican aliens will gladly take. Those positions are in agriculture, factories, hotels, and restaurants. While these may be low-paying jobs, she says, ''making very few dollars is better than making very few pesos.''