WASHINGTON (Reuters) - As another U.S. government funding deadline looms, a huge spending bill is ground zero in the latest battle between Republicans and Democrats in Congress over President Donald Trump’s push to toughen immigration policy.

Lawmakers have until March 23 to work out how to fund an array of government agencies for the next six months. But their behind-the-scenes negotiations are complicated by the immigration issue.

Republicans are seeking hundreds of millions of dollars more for the Department of Homeland Security to expand the number of beds for immigrant detainees and to hire more federal agents to patrol U.S. borders and the country’s interior.

That is aimed at finding and potentially deporting more illegal immigrants, a central pledge of Trump’s 2016 presidential campaign.

“If you increased the number of beds, the number of people detained in this country will likely be increased,” said Sarah Pierce, a policy analyst for the non-partisan Migration Policy Institute.

She said that would help Trump carry out initiatives to expand detentions, including possibly those of children who are in the country illegally. For some immigrants, it could mean spending as long as two years in detention while their cases wind through an overburdened court system, instead of being under looser government controls during the process.

Congressional negotiators also are tussling over a Republican provision prohibiting the use of U.S. Immigration and Customs Enforcement funds to facilitate abortions for immigrant detainees.

There is also a push for $1.6 billion to begin construction on a border wall, which Trump promised during his campaign would be paid for by Mexico - an unwilling partner in that pledge. That would be a down payment on a construction project likely to end up costing more than $18 billion.

During a visit to California on Tuesday, Trump inspected wall prototypes and urged Congress to fund it.

FILE PHOTO: The United States Capitol Dome is seen before dawn in Washington March 22, 2013. REUTERS/Gary Cameron

House Judiciary Committee Chairman Bob Goodlatte, an advocate for Trump’s immigration agenda, told reporters on Wednesday, “If there are additional appropriations added, I certainly would be supportive of that.”

Democrats, whose votes in the Republican-controlled Congress are likely needed to pass the trillion-dollar spending bill, are pushing back against a wall that they see as a waste of money.

A coalition of 83 Hispanic, African-American and Asian-American members of the House of Representatives wrote this week to congressional leaders urging them to also “reduce funding to DHS’s detention and deportation machine.”

Democratic Representative Michelle Lujan Grisham, who heads the Congressional Hispanic Caucus, told reporters: “It’s wasteful and it’s harmfully targeting and deporting non-criminal immigrants, separating families and terrorizing frankly whole communities.”

BATTLEGROUND

Appropriations bills in Congress are the lifeblood of Washington policymakers, providing the money to carry out their priorities.

Over the past several months, appropriations bills to fund an array of federal programs have been the battleground in which Trump and Congress fought over the future of young people brought to the country illegally as children.

That six-month skirmish ended last month with Congress unable to legislate new protection from deportation for 700,000 “Dreamers” after Trump ended an Obama-era program giving them temporary legal status. At one point, the standoff forced Washington into a three-day government shutdown in January when funding ran out.

This time, Republicans hope to get enough money to hire 500 more Customs and Border Protection agents and 1,000 more Immigration and Customs Enforcement officials. That would be the start of an eventual increase of CBP’s workforce by 5,000 and ICE’s by 10,000.

Democrats have noted that the agencies are falling short in filling all positions Congress already has authorized.

Negotiators are expected to work through the weekend as House of Representatives leaders hope to unveil a bill early next week so it can be debated on the House floor by midweek, with a Senate vote by the March 23 deadline.

Failure to meet the deadline could result in the second partial government shutdown this year.