We are also beginning to hear more frequently about "dual citizenship," but that phrase is an oxymoron. One cannot truly be a citizen of two different countries because ultimately loyalty cannot be divided.

If the two countries went to war against each other, the so-called dual citizens would have to pick sides. No man can serve two masters: for either he will hate the one, and love the other; or else he will hold to the one and despise the other.

Dual citizenship is not the same as holding two active passports from different countries, because a passport alone does not confer citizenship. Getting a U.S. passport does not require you to forfeit passports from other countries.

The issue of dual citizenship arises because countries have different requirements for citizenship and it is possible to satisfy the requirements of two or more countries. U.S. citizenship is based on U.S. law, which is that one must be born in the United States or naturalized according to our naturalization law.

Everyone who is naturalized as a U.S. citizen must swear this solemn oath: "I hereby declare, on oath, that I absolutely and entirely renounce and abjure all allegiance and fidelity to any foreign prince, potentate, state or sovereignty, of whom or which I have heretofore been a subject or citizen; that I will support and defend the Constitution and laws of the United States of America against all enemies, foreign and domestic; that I will bear true faith and allegiance to the same; that I will bear arms on behalf of the United States when required by the law . . ."

Thus, in order to become a U.S. citizen, immigrants are required by law to transfer their allegiance from their native country to the United States of America. But our country is now confronted with the problem of immigrants who have been falsely led to believe that they are or can be dual citizens, and this dangerous notion is diluting our national identity and culture.

Mexico passed a law in 1998 that extends citizenship to Mexicans who are naturalized in other countries and to their children. This is an invitation to new U.S. citizens either to betray their oath of allegiance to the United States or to cross their fingers behind their backs when they take it.

Many statements by President Vicente Fox and other Mexican officials show that their plan is to export a segment of their population to the United States, let them become U.S. citizens, but retain them as Mexican citizens. Mexico wants these new American citizens to consider themselves "binationals," and to vote in both the U.S. and Mexico, with Mexican politicians campaigning for their votes and allegiance.

Mexico is also trying to legitimize Mexican aliens illegally living in the United States by giving them special ID cards called "matricula consulare." These Mexican ID cards are being used to pretend to validate their illegal residence, prevent deportation, and help them to get U.S. driver's licenses, jobs, taxpayer benefits, and in-state university tuition.

U.S. officials from San Francisco to Anaheim, Albuquerque to Austin to Houston, have announced that they will accept these Mexican- issued ID cards. Some police, some banks, and some airlines have said they will accept them.

U.S. law allows U.S. citizenship to be removed if a person behaves like a citizen of another country or manifests an intent to give up U.S. citizenship as shown by statements or conduct. But a series of post-World War II U.S. Supreme Court 5-4 decisions have made it difficult to revoke U.S. citizenship.

Current law specifies at least seven reasons for revoking U.S. citizenship, such as obtaining naturalization in a foreign state or taking an oath to a foreign state. Voting is not one of the listed reasons.

We are told that millions of U.S. residents now claim dual citizenship. Congress should put an end to this dangerous notion and tighten up the law on what constitutes evidence that a naturalized U.S. citizen intends to retain or to reinstate his loyalty to a foreign country.

Congress could, for example, legislate that voting in a foreign country is evidence of intent to relinquish U.S. citizenship. Congress should also authorize our government to revoke citizenship based on the preponderance of evidence standard.