Members of the U.S. Senate are considering two competing proposals aimed at reforming immigration policy. The lawmakers, particularly those from states that border Mexico, are alarmed by the numbers of illegal immigrants entering the United States every year.

Although the actual number of illegal immigrants who come into the country each year is not known, the Department of Homeland Security says more than one million people were apprehended last year entering the United States illegally from across the Mexican border, as compared to 10,000 trying to cross the border with Canada.

The agency says most of those trying to cross into the United States from Mexico were Mexicans, who were attempting the trip for economic reasons or to join family members. But the department says there are a growing number of people from other countries, whom the agency identifies as other than Mexicans, or OTMs, who also attempt illegal entry in the United States from the Mexican border.

"Currently, we are seeing about a 131 percent increase in the area of OTMs coming into our country. So far this year, we have detained approximately 119-thousand other-than-Mexicans coming across our nation's border with Mexico," said border patrol chief David Aguilar in testimony before the Senate Foreign Relations Committee earlier this month.

Several thousand of them were from so-called countries of interest, including Somalia, Pakistan and Saudi Arabia, which have been associated with terrorist cells.

Lawmakers are concerned about the potential for terrorists to enter the United States undetected across the border with Mexico.

But they are also concerned by the impact that growing numbers of illegal aliens could have on U.S. health care and other social services.

Senator John McCain, a Republican from Arizona, a state which borders Mexico, says current immigration policy is unacceptable because it forces Mexican nationals and others illegally seeking to enter the United States to rely on human smugglers or risk their lives crossing the desert border area alone. He also says porous borders are leaving Americans vulnerable to terrorism.

"It is obvious that this is a national security issue, it is an economic issue, and it is a humanitarian issue. We need to act," he said.

Senator McCain has joined with Senator Ted Kennedy, a Massachusetts Democrat, in introducing a bill that aims to reform the immigration system by allowing millions of illegal immigrants in the United States to apply to be temporary guest workers and permits residents of other countries to seek the same status if they can prove that a job is waiting for them.

Mr. McCain and Mr. Kennedy discussed the legislation at a Senate Judiciary Committee hearing Tuesday.

Under the bill, millions of illegal workers and immigrants who want jobs in the United States could eventually gain citizenship, although it is not a guarantee.

But the measure faces resistance from many Republicans who argue it is an amnesty proposal, an assertion Mr. McCain rejects.

Senator John Cornyn of Texas has co-sponsored an alternate proposal with the other Republican senator from Arizona, Jon Kyl. That measure would allow people from other countries to work in the United States for up to two years before returning home. It also would require the millions of illegal immigrants already in this country to return home before applying to join the program.

"Our proposal requires undocumented workers in the United States to register and go through the normal immigration process. It is true they must depart the United States temporarily, but they may then, if they qualify, reenter the country with a legal status," said Senator Cornyn.

Senator McCain says that plan is just not realistic. "The reality is, 11 million people are not going to voluntarily come out of the shadows just to be shipped home," he said. "Report to deport is not a reality, and it is not workable. Systematically rounding up every person living here illegally and sending them home is not a viable option, either. It is neither practically possible nor economically feasible," he said.

A study released by the liberal Center for American Progress Tuesday estimates the cost of forcibly removing most of the nation's illegal immigrants at $41 billion a year. The study of the costs associated with the arrests, detentions, prosecutions and removal of illegal immigrants was conducted in response to calls from conservative politicians for mass deportations.

It is not clear whether the Senate and the House of Representatives, which is considering its own proposals, will complete immigration reform this year.

Some in the Republican majority in Congress have expressed frustration that the Bush administration has not done more on the issue.

But administration officials are divided over the best way to reform the immigration system.

In fact, the administration withdrew the two witnesses who had been scheduled to testify at Tuesday's hearing, Homeland Security Secretary Michael Chertoff and Labor Secretary Elaine Chao. No explanation was given for their absence.