UNWITTINGLY, THE leader of a local group whose self-appointed mission is to photograph, spy on and bother undocumented day laborers in the town of Herndon, put his finger on the dilemma of illegal immigration the other day. "What we want, bottom line in Herndon, is for the illegal aliens to leave," said George Taplin, leader of the town chapter of the Minuteman Project, a national organization bitterly opposed to illegal immigrants. "And if there is no work, they will."

Ah, but there you have the problem: There is work -- enormous amounts of work, particularly in the Northern Virginia suburbs. In fact, in an area with virtually no unemployment, the market is desperate for immigrant labor, documented, undocumented or falsely documented. It helps keep the economy growing, and immigrants come here because they know they are needed and there will be plenty of work. Anti-immigrant crusaders such as Mr. Taplin may not like it, but unless they have discovered a magic formula for shrinking the regional economy in boom-'burbs such as Fairfax County, no amount of spying on, photographing or hassling undocumented day laborers and their employers will eliminate this irrepressible demand for labor.

Of course, anti-immigration cranks such as the Minutemen know that, so what they are really up to is simple harassment. They train their still and video cameras on day laborers with families to feed and rents to pay and on the employers that pick them up for work. They jot down license-plate numbers and talk to each other with walkie-talkies. They convey the information they collect to the Internal Revenue Service, which, to put it mildly, has bigger fish to fry.

Reveling in self-importance, the Minutemen and their ilk say they are plugging enforcement gaps that the federal government has left open. In fact they are underemployed amateurs more interested in posturing than problem-solving. In Vermont one such group got lost in the woods while hunting for undocumented infiltrators and had to ask for directions, the Boston Globe reported. Some spent their Saturday "patrol" sitting in lawn chairs in a field, staring at a tree line. People like these would dearly love to deport all 11 million undocumented immigrants. But that's not going to happen.

Rather than harassing undocumented workers and staring at trees, the Minutemen should heed Dean Boyd, spokesman for U.S. Immigration and Customs Enforcement. He told The Post's Karin Brulliard: "Law enforcement is best left up to professionals."