By Richard Cowan and Susan Cornwell

WASHINGTON (Reuters) – The White House stuck to its hard-line immigration approach on Thursday and said advisers would recommend that President Donald Trump veto a bipartisan U.S. Senate proposal to protect young “Dreamer” immigrants and tighten border security.

The plan, which would protect from deportation 1.8 million young adults who were brought to the United States illegally as children, would weaken border security and undercut existing immigration law, spokeswoman Sarah Sanders said in a statement.

“Preventing enforcement with respect to people who entered our country illegally before a date that is in the future would produce a flood of new illegal immigration in the coming months,” she said.

The proposal, which had been considered perhaps the most likely to succeed in the Senate, also includes a $25 billion fund to strengthen border security and possibly even build segments of Trump’s long-promised border wall with Mexico.

White House opposition to the bipartisan plan appeared to focus on a provision that would direct the Department of Homeland Security to focus enforcement efforts on undocumented immigrants who have been convicted of crimes, are a threat to national security or arrived in the United States after June 30, 2018.

The Senate is debating at least four immigration measures as lawmakers race to resolve the status of Dreamers, who were protected under an Obama-era program. Trump has ordered that program to end by March 5, telling Congress it should come up with an alternative plan by then.

The Department of Homeland Security also opposed the bipartisan plan led by Republican Senator Susan Collins, saying it would prevent DHS officers from being able to remove millions of undocumented immigrants from the country, and “is an egregious violation of the four compromise pillars laid out by the President’s immigration reform framework.”

Trump has said any immigration bill must include funds to build the border wall, end the visa lottery program, impose curbs on visas for the families of legal immigrants and protect Dreamers.

The Republican president has backed a measure by Republican Senator Chuck Grassley that embraces his wish list but is unlikely to win support from enough Democrats in the closely divided chamber.

A narrower third bill focusing just on Dreamers and border security, by Republican John McCain and Democrat Chris Coons, has been dismissed by Trump. A fourth measure, which is not expected to pass, focuses on punishing “sanctuary cities” that do not cooperate with federal immigration enforcement efforts.

Senate Majority Leader Mitch McConnell said votes on the four measures would be held possibly on Thursday or at least Friday morning, ahead of a self-imposed Senate deadline of the end of the week.

‘BITTER PILLS’

The bipartisan Collins bill got a slight boost earlier on Thursday when an influential group that advocates for immigrants, America’s Voice, gave its reluctant support to the measure.

The group opposes provisions allowing the construction of a border wall and moves to limit legal immigration, but said in a statement, “We believe the chance to provide a permanent solution for Dreamers calls us to swallow these bitter pills.”

Despite backing from several Republicans for the Collins-led plan, it was unclear whether it would muster the 60 votes needed in the 100-member Senate, controlled 51-49 by Republicans.

A senior Senate Republican aide said the White House veto threat would “scuttle” some Republican support for the bipartisan bill. The prospect of all bills failing could even discourage some Republicans from voting for the Trump-backed plan, the aide said.

Trump is anxious to start on the border wall, which he made a central part of his 2016 election campaign and which Democrats have long opposed. Senate Democratic Leader Chuck Schumer said the wall would be “an enormous waste of money,” but both parties had to bend.

“We have to rise above our differences, admit that no one will get everything they want and accept painful compromises,” Schumer said.

In September, Trump rescinded the Deferred Action for Childhood Arrivals (DACA) program to protect Dreamers from deportation and offer them work permits. Although the protections are due to start expiring on March 5, federal judges have blocked that from taking effect amid ongoing litigation.

Even if one of the Senate measures passes, it must still win over the U.S. House of Representatives, where Republicans hold a larger majority and are pushing a more conservative proposal that is more closely in line with Trump’s framework.

(Additional reporting by Susan Heavey and Makini Brice; Writing by John Whitesides; Editing by Frances Kerry)