President George W Bush has made a personal appeal to his own party's senators in an attempt to win support for controversial immigration reforms.
President Bush is keen to overhaul immigration laws this year
Speaking after a rare visit to Senate Republicans on Capitol Hill, Mr Bush said he understood there were divisions within the party, but urged action.
"Now is the time to get it done," he said. "The status quo is unacceptable."
A proposed immigration law bill stalled last week after the Senate failed to vote to make progress on the measure.
The main stumbling block was opposition from all but a handful of Republicans.
The deadlock followed a series of amendments to the proposed bill, which undermined a fragile bipartisan compromise.
The bill would have tightened border controls, but given 12 million illegal immigrants already in the US a way to legal status and citizenship.
Mr Bush's unusual trip to the Republican senators' policy luncheon underscored the importance he has placed on overhauling US immigration laws before his term ends.
Illegal immigration is among voters' top concerns and is set to be a key issue in the 2008 presidential poll.
Mr Bush, who wants to see immigration laws overhauled this year, has said he believes the proposed legislation can pass.
But he faces substantial opposition from Republicans, many of whom say they need more time to debate the proposed legislation and argue it should be tougher.
Speaking after his visit to the Senate Republicans' lunch, Mr Bush said: "It's going to take a lot of hard work, a lot of effort.
"We've got to convince the American people that this bill is the best way to enforce our border."
He acknowledged that not everyone agreed on what was "a highly emotional issue" but said he wanted to thank those senators in both parties who were ready to back comprehensive reform.
Republican Senator Jeff Sessions told CNN that Mr Bush needed to "back off" and give senators the time to make sure that whatever bill was passed would work.
Democratic Senate Majority Leader Harry Reid withdrew the legislation last Thursday after two failed attempts to bring it to a final vote - but has said he will bring it back if confident of enough Republican support.
Mr Bush pressed him to keep up momentum on the bill.
The bipartisan Senate bill had elements which were hard for both Democrats and Republicans to accept.
The immigration debate is proving divisive in Congress and the nation
Some critics called it an "amnesty" for those who had illegally entered the US, while other opponents argued its guest worker programme threatened American workers.
Under the proposed Senate bill, illegal immigrants could seek a renewable "Z visa" after paying a $5,000 (£2,530) fine.
They could ultimately be placed on the path to permanent residency - a process that could take several years.
The bill also set out a "points system" that emphasises immigrants' education, language and job skills over family connections in awarding green cards.
But these measures would not come into force until 18,000 new border guards are deployed, the fence with Mexico reinforced and hi-tech surveillance put in place.
Some Democrats say the bill would destroy families, because people's employment prospects, rather than links to relatives already in the United States, would be a key criterion in allocating visas.
The House of Representatives, where views on immigration reform are even more polarised, has still to consider its version of the legislation.