The U.S. Senate has begun debate on immigration reform, an issue that could impact this year's congressional elections.

The Senate began considering new efforts to secure the U.S. border with Mexico and a proposal to create a guest worker program, which offers the nation's estimated 11 million illegal immigrants an opportunity to become permanent residents and eventual American citizens.

But majority Republicans are divided over the guest worker proposal. Senate Majority Leader Bill Frist argues the plan rewards those who enter the United States illegally.

"I disagree with this approach, not just as a matter of principle, but because granting amnesty now will only encourage future and further disrespect for the law," said Bill Frist. "It will undermine our efforts to secure our homeland."

Frist, a likely presidential candidate in 2008, has introduced legislation that focuses on border security and efforts to stop illegal immigrants from working, but does not include a guest worker program.

Another Republican, Senator Arlen Specter of Pennsylvania, is to introduce separate legislation Thursday that includes border security provisions but also a guest worker program, which President Bush supports. Specter, who chairs the Judiciary Committee, took issue with Frist's characterization of the guest worker proposal:

"I want to disagree with him head-on: it is not amnesty," said Arlen Specter. "It is not amnesty because the law-breakers are not being unconditionally forgiven for their transgressions."

The guest worker program is a challenging issue for Republicans ahead of November congressional elections. Many do not want to anger members of the conservative base of their party, who oppose the plan. But at the same time, they do not want to lose support among the increasingly influential Hispanic electorate or the business community, which depends on undocumented workers for low-wage jobs.

Democrats generally support a guest worker program. But their allies in the AFL-CIO labor federation oppose it, saying it would cast workers into a second-class status.

The outcome of the Senate debate is far from clear. Any legislation approved by the Senate would have to be reconciled with a House-passed bill, which does not include a guest worker program.