WASHINGTON (REUTERS) - Congressional leaders arrived at the White House on Wednesday (Jan 2) for a briefing in which President Donald Trump and homeland security officials will press their case for a border wall as he held fast to his demand for US$5 billion (S$6.8 billion) in wall funding that triggered a partial government shutdown now in its 12th day.

Trump said the shutdown affecting about a quarter of the federal government and 800,000 federal workers would last for "as long as it takes" as he pushes lawmakers for money for a wall along the US-Mexico border as part of any legislation to reopen agencies shuttered when their funding lapsed on Dec 22.

"It could be a long time," Trump told reporters during a Cabinet meeting, "or it could be quickly."

The Cabinet meeting came ahead of a border security briefing behind closed doors in the White House Situation Room - generally used for high-level security concerns such as military planning - for congressional leaders by US Department of Homeland Security officials.

Trump said he was open to working on a path to legal status for hundreds of thousands of young illegal immigrants known as Dreamers, pointing toward a potential broader deal with Democrats that could resolve the shutdown.

Trump made the border wall a key part of his presidential campaign and tried again to make a case for it shortly before lawmakers arrived for the afternoon briefing.

He called the border a "sieve," rebutted Democratic complaints that a wall was immoral, provided an estimate of the US illegal immigrant population far higher than the figures most experts cite and made disputed comments about progress toward building a wall.

Democrats take charge of the House of Representatives from Trump's fellow Republicans when the new 2019-2020 Congress convenes on Thursday.

Led by presumptive House Speaker Nancy Pelosi, they have scheduled votes on their first day in the majority on legislation that would end the shutdown without providing the wall funding Trump wants.

Republicans retain control of the Senate.

The visit by Pelosi and Democratic Senate leader Chuck Schumer was their first to the White House since their sharp exchange with Trump in the Oval Office on Dec 11 during which the president told them he would be "proud to shut down the government for border security."

He has since blamed Democrats for the shutdown.

Trump's demand for the wall funding thwarted congressional efforts to pass federal funding legislation last month. Democrats oppose the wall and Trump's funding demand.

'SO INSIGNIFICANT'

The US$5 billion Trump is seeking would cover only a portion of the money needed for a border wall, a project estimated to cost about US$23 billion. Trump had said Mexico would pay for the wall but Mexico has refused.

When asked by a reporter if he would accept less than US$5 billion, Trump said: "I'd rather not say it. Could we do it for a little bit less? It's so insignificant compared to what we're talking about."

After a White House meeting on Sunday, Republican Senator Lindsey Graham said Trump was receptive to Graham's idea of a deal that might provide work permits to Dreamer immigrants in exchange for money for physical border barriers.

Federal courts have blocked Trump's effort to end a programme begun in 2012 under Democratic former President Barack Obama that protected the Dreamers, who were brought into the United States as children, from deportation and gave them work permits.

Trump's administration asked the US Supreme Court in November to allow the president to end Obama's Deferred Action for Childhood Arrivals, or Daca.

Speaking during the Cabinet meeting, Trump said he was sure the Supreme Court would side with him and that the administration would then be able to make a deal easily on the Dreamers and the wall.

Trump said US Immigration and Customs Enforcement and border patrol officials will make a plea for a wall at the meeting.

Prospects for the two-part Democratic spending package that will be voted upon in the House appear grim in the Senate. The measure sets up the first major battle of the new Congress between House Democrats led by Pelosi and Republican Senate Majority Leader Mitch McConnell, who has said Senate Republicans will not approve a spending measure Trump does not support.

White House spokeswoman Sarah Sanders in a statement late on Tuesday called the Democratic plan "a non-starter."