Latin will never be a truly dead language -- at least not as long as "E pluribus unum" appears on our money. That's our national motto: "Out of many, one." We've always been willing to open our arms to immigrants and help them become Americans.

But the unity we once valued is unraveling.

In the past, new Americans were welcomed with a solemn ceremony that matched the commitment they were making to their adopted homeland. But today's new citizens have no such uplifting experience.

To qualify they need only pass a standardized, multiple-choice test, often given in their native tongue. In fact, they're not required to show much knowledge of English. If they can transcribe just one of two dictated sentences (correct spelling and punctuation don't count), that's enough to merit citizenship.

And the greater problem is that too many people don't even go that far. Millions of foreigners are living here today with no expectation of ever becoming citizens. They're illegal immigrants.

It's impossible to know exactly how many people are here illegally. But the Pew Hispanic Center, a Washington-based research group, estimates the United States hosted 10.3 million illegal immigrants in 2004, up from an estimated 8.4 million four years earlier. That's an awful lot of people doing all they can to avoid the American melting pot.

Illegals aren't coming here to take in the scenery; they're coming to work. So the best place to fight illegal immigration is on the supply side.

Employers are already required to collect Social Security numbers from everyone they hire and to withhold state and federal taxes from everyone's wages. The federal government could start addressing the problem by cracking down on employers who hire illegals.

We also should make it easier for employers to fill vacancies legally, by starting a guest-worker program that uses private-sector expertise to supply documented workers. One way to do this is to allow job agencies, licensed by the government, to set up shop in foreign countries and issue worker visas to qualified applicants. Employers then could hire the pre-screened foreigners, confident that they're hiring legal workers.

We now have the technology to track guest workers while they're in the United States. Muslims traveling to Mecca for the Hajj have their retinas scanned on the way into Saudi Arabia and on the way out, so the Saudis know exactly who's in their country. Similarly, guest workers here could receive an ID card and be subject to a similar scan at any time, thus ensuring they don't overstay their welcome.

While implementing these measures, the United States should take steps to improve economies south of the border.

Workers flock to the United States because they think that, even as illegals, they can make more money here than if they were to remain at home. Sadly, they're usually right, which explains the virtual flood of humanity coming across our southern border.

But it's possible to change that. U.S. foreign policy should encourage Latin American countries to open their economies by selling off government-run industries and help their governments create a climate that respects individual rights.

Doing so would help countries such as Mexico create more jobs, something it desperately needs to do. On average, Mexico has created a mere 500,000 jobs in each of the last five years, not nearly enough to make a dent in its unemployment rate. If Mexico can improve its economy, though, people will have a reason to stay in their native land.

The United States is, and will remain, the land of opportunity. But we can't afford to tolerate an underground economy, populated by immigrants who are unwilling or unable to assimilate. By cracking down on illegal immigration in a smart way, we can continue our tradition of turning many into one.

Ed Feulner is president of The Heritage Foundation (heritage.org), a Washington-based public policy research institute.