April 6 (Bloomberg) -- Senate Republicans and Democrats reached an agreement on procedures for allowing undocumented aliens to apply for citizenship, clearing an obstacle that stalled legislation overhauling U.S. immigration laws.

``We have a huge breakthrough,'' Senate Majority Leader Bill Frist of Tennessee told reporters today.

Democrats, including Senator Ted Kennedy of Massachusetts and Minority Leader Harry Reid, said the compromise may lead to passage of the Senate measure this week.

``Hopefully in the next 24 hours there will be a real celebration,'' Reid said. President George W. Bush supports it too and will publicly endorse it later today, said Arizona Senator John McCain.

The compromise splits the estimated 11 million undocumented immigrants into three groups, based on how long they have been in the U.S., for the purpose of setting rules on their eligibility to apply for legal status.

Under the plan hammered out by Republicans last night, the more than 1 million undocumented immigrants who entered the U.S. after Jan. 7, 2004, would have to return to their home countries and apply for a new guest-worker program from there.

The estimated 3 million immigrants who illegally entered between 2001 and 2004 would have three years to apply for legal status as part of a new temporary-worker program and pay as much as $3,000 in fines. To receive their temporary-worker visas, they would have to travel to a land port of entry and physically leave the U.S. before immediately re-entering.

Once they receive the visas, they could stay as long as six years while applying for one of 130,000 permanent residency cards set aside annually for the group. If they don't win permanent residency after six years, they would have to leave.

More Than Five Years

Undocumented immigrants who have been in the U.S. more than five years, an estimated 7 million people, would be able to keep their jobs after paying a $2,000 fine and meeting other criteria, such as learning English.

Before a two-week recess begins at the end of this week, the Senate is working to pass an overhaul of immigration policies that includes strengthening border security and creating a guest- worker program. Debate on the measure had stalled as Republicans negotiated how to treat undocumented immigrants and Democrats worked to block amendments they said were too harsh.

The House last year passed legislation that increases border security without addressing a guest-worker program or allowing undocumented immigrants to apply for legal status. Any Senate measure would have to be merged with the House proposal.

Some Republicans said they remain opposed to the plan. ``It's unacceptable to me,'' Republican Jeff Sessions of Alabama said. ``We're not ready to do this right now.''

Paying a Fine

Republicans Mel Martinez of Florida, Chuck Hagel of Nebraska, Lindsay Graham of South Carolina and McCain spent days negotiating before agreeing on this proposal.

Under the agreement, all undocumented immigrants in the U.S. for more than five years would be able to acquire legal residency and U.S. citizenship after about 11 years.

The compromise doesn't change guest-worker proposals that would allow 400,000 immigrants each year to enter the U.S. for jobs.

Frist said senators will have the opportunity over the next two days to vote on three separate immigration proposals. They are the compromise introduced last night; Frist's own legislation that focuses on border security and enforcement of immigration laws; and a Judiciary Committee measure that lets undocumented immigrants in the country before Jan. 7, 2004, apply for legal status and stay at their jobs in the U.S. after paying a $1,000 fine, passing a background check and learning English.

The votes will ``allow people to express where they are,'' Frist said last night. ``We can't predict the outcome.''

Democrats today failed to gain the 60 votes necessary to limit debate on the committee proposal. Thirty-nine Senators voted to end debate with 60 voting against it.