Think the immigration debate is mainly about giving amnesty to the 10 million illegals already here? Think again. Amnesty is a drop in the bucket. The real issue is the staggering increase in legal immigration hidden in the Comprehensive Immigration Reform Act, recently passed in the Senate.

By a ratio of about 4-1, U.S. voters would prefer less immigration, not more. But the Senate bill would do just the opposite. The original bill would have allowed as many as 100 million people to legally immigrate to the United States over the next 20 years. We're talking about a seismic shift of unprecedented proportions.

Facing criticism, the Senate has amended the bill - which now would allow "only" 61 million new immigrants. That still more than doubles the current legal immigration rate, from 1 million a year now to 2.5 million.

Current law would let 19 million legal immigrants enter the United States over the next 20 years; the Senate immigration bill would add an extra 42 million.

Why such extraordinary growth? Consider how the new law would work.

Under the Senate bill, immigrants could enter or attain lawful status within the country through nine channels. In each channel, immigrants would gain permanent residence and the right to become citizens:

Current law visas: About 950,000 persons now get permanent-residence visas every year under current law. Over 20 years, the inflow of immigrants through this channel would be 19 million.

Amnesty: The bill would grant amnesty to roughly 10 million illegal immigrants now living in the U.S.

Spouses/children of illegal immigrants given amnesty: Illegals who got amnesty could bring their spouses and children into the country as legal permanent residents with the opportunity for full citizenship. The resulting number of spouses and children who would enter the United States? At least 5 million.

"Family chain" migration: Today's law limits the number of kinship visas for secondary family members, such as adult brothers and sisters. The Senate bill would raise the cap on such secondary family immigration from around 230,000 to 480,000 per year, bringing in 5 million new immigrants over 20 years.

Temporary guest workers for life: The amended Senate bill would let 200,000 people enter through the guest-worker program each year. Over 20 years, that works out to a total inflow of 4 million. The "guest workers" aren't temporary at all, but could stay in the U.S. permanently and become citizens.

Spouses/children of guest workers: Guest workers could bring their spouses and children to the United States as permanent residents, adding another 4.8 million entrants over 20 years.

Worker visas for skilled specialty occupations: The Senate bill would initially double the number of specialty workers who could enter the U.S., and would then allow the number to increase by 20 percent in each subsequent year. These workers would be permitted to request permanent residence, and, in most cases, would be able to stay in the U.S. for life. More than 5.5 million legal immigrant workers could enter under these provisions over the next two decades.

Spouses/children of specialty workers: Specialty workers could bring their spouses and children to the United States as permanent residents, adding another 3 million entrants over 20 years.

Refugee women: Under the bill, an unlimited number of women who fear they may undergo "harm" as a result of their sex may enter the U.S. as refugees and become citizens. The numbers who would enter under this open-ended provision is uncertain, but 1 million over 20 years is a reasonable estimate.

Parents of naturalized citizens: The Senate bill would greatly increase the number of naturalized citizens, each would have an unlimited right to bring their parents into the country as legal permanent residents. The resulting number of parents who would enter as permanent legal residents? Around 3.5 million over 20 years.

If the Senate bill became law, foreign-born immigrants would rise to around 18 percent of the total U.S. population, an immigration level far higher than at any previous time in U.S. history.

Many in this looming tidal wave of immigration would be low-skilled individuals who will impose great social and economic costs on the nation. For example, more than half of the 10 million illegals who will get amnesty are high-school dropouts; on average, each immigrant dropout will cost the U.S. taxpayers $85,000 over the course of his life.

In sum, the Senate bill would bring profound change, transforming the United States socially, economically and politically. Within two decades, the character of our country would differ dramatically from what exists today.

Americans need to ask: Is that what we want?

Robert Rector is a Senior Research Fellow in Domestic Policy Studies at the Heritage Foundation.