Americans, the most recent CBS/New York Times poll found, hold a nuanced set of views on immigration reform.

The percentage saying that the level of legal immigration should remain the same or increase now stands at 59%, the highest level ever recorded. Over half (53%) believe illegal immigrants work in the sort of gritty jobs that native-born Americans shun. An even larger percentage (61%) wants to give illegals who have lived and worked here for two years or more a chance to apply for citizenship rather than be deported. Two-thirds say they oppose building a 700-mile fence along the U.S.-Mexican border.

Yet nine out of 10 believe that, on balance, illegal immigration poses serious problems that Congress must address. What explains these seemingly inconsistent views?

The answer lies in the question that elicited the strongest response. Asked whether illegal immigrants strengthen the economy because they "provide low-cost labor and spend money" or harm it because they "don't all pay taxes but can use public services," an overwhelming 70% said they believe illegal immigrants create a drain on our economy.

According to Heritage Foundation welfare expert Robert Rector, the overwhelming majority of Americans has it right. Rector reviewed the economic literature on the fiscal effects of immigration and found that the skills level of those awarded citizenship is a crucial factor in assessing their fiscal impact. It's positive for immigrants with some college education, mixed for those with a high-school degree, and negative for high-school dropouts. "This is important," Rector notes, "because half of adult illegal immigrants in the U.S. … have less than a high-school education."

Indeed, Rector reports that over the past four decades the educational level of new immigrants has fallen steadily relative to that of native-born Americans, as have their wages and the rate at which their children and grandchildren achieve economic success. Coupled with very high levels of out-of-wedlock birthrates (among foreign-born Hispanics, for example, the rate is 42.3%), the current illegal population fits the classic profile of a group that, if offered a ready route to citizenship, will consume billions more in welfare benefits than they will contribute in taxes.
The historical pattern whereby new immigrants claim fewer welfare benefits than native-born Americans reversed itself about three decades ago as the size and reach of the welfare state grew. In just the last five years, enrollments in welfare programs have skyrocketed. Medicaid enrollment has grown by 50%, Food Stamps by 49% and Pell Grants by 33%. The earned income tax credit program now provides generous subsidies (over $35 billion annually) to more than 21 million low-wage workers.

Not surprisingly, legal immigrant households are now 50 percent more likely to receive welfare benefits than are the native-born. Immigrants without a high-school degree, moreover, were two and a half times more likely to enroll in these programs. "This underscores," Rector concludes, "the high potential welfare costs that may be associated with proposed amnesties to illegal immigrants."

How high? The leading congressional plan to resolve the impasse over illegal immigration, introduced by Sens. Chuck Hagel (R-Neb.) and Mel Martinez (R-Fla.), would offer amnesty and, ultimately, citizenship to between 60% and 85% of the 12 million illegal population at an annual cost that Rector estimates at between $11.4 billion and $16 billion.

And this estimate only looks at the illegal population already here. With citizenship comes the unrestricted right to bring one's spouses, minor children and even parents to America, each of whom would be eligible for citizenship. And that, in turn, confers the unrestricted right to avail oneself of all welfare programs that have ensnared millions in the poverty trap.

Overall, the "family chain migration" envisioned in the Hagel-Martinez proposal could cost additional tens of billions per year, much of it in emergency room and hospital costs borne by Medicaid.

It gets worse. Under Hagel-Martinez, 325,000 new visas would be issued annually for "guest workers." Nearly all of these workers and their families would become eligible for -- you guessed it -- welfare benefits. The fiscal consequences of allowing each guest worker to import an entourage of relatives could rival those of the amnesty program itself.

The legislation that Senate may soon consider would create no fewer than six channels through which tens of millions of additional immigrants could enter the U.S. and become citizens, a disproportionate number of whom fit the demographic profile of our current welfare population. If lawmakers want future immigrants to be net contributors to rather than a net burden, they must make immigration policy favor workers with higher levels of education and better job skills.

Mike Franc, who has held a number of positions on Capitol Hill, is vice president of Government Relations at The Heritage Foundation.