Factbox: What happens if Homeland Security funding lapses?

(Reuters) - Congress is embroiled in a battle over a $39.7 billion funding bill for the Department of Homeland Security, which is charged with securing U.S. borders, airports and coastal waters.

House Republicans have passed a budget bill that would ban spending on President Barack Obama's immigration initiatives. With a Feb. 27 deadline looming, Democrats have blocked the Senate from considering that bill in three separate votes.

Republicans say Obama would take the blame for putting U.S. national security at risk if DHS funds are cut off. And some conservatives downplay the consequences, saying there would be no interruption in the agency's critical protective missions.

The following is a rundown of what would likely happen if DHS spending authority is allowed to expire on Feb. 27, based on the agency's own contingency plans and congressional researchers.

DON'T CANCEL THAT FLIGHT

Most DHS employees would stay on the job, especially those involved in securing and protecting airports, borders and other ports of entry into the United States.

Transportation Security Administration passenger screenings and the Federal Air Marshal Service would continue uninterrupted as would Coast Guard operations and disaster relief.

In all, DHS has designated about 85 percent of its workforce, or around 200,000 people, as 'exempt' from furlough because they are involved in protecting human life and property or are funded by other sources, such as customs fees.

But while these people would be required to work, many of them would not be paid until a new funding bill is signed into law.

TENS OF THOUSANDS IDLED

DHS has said it expects to idle about 30,000 employees not serving in front-line operations. Activities such as procurement, hiring, training and administrative support would be hardest hit.

DHS said "the bulk" of its management would be furloughed, including many people dedicated to improving command and coordination of domestic anti-terrorism activities.

E-Verify, an automated computer system that companies use to check the citizenship and visa status of prospective employees, would be shut down, hampering some hiring activities.

IMMIGRATION AGENCIES

U.S. Citizenship and Immigration Services, targeted by Republican efforts to block Obama's 2012 and 2014 immigration orders, would ironically be the least affected by a DHS funding lapse. It would keep 98 percent of its roughly 12,500 employees on the job because it is funded almost entirely from fees paid by applicants, according to the Congressional Research Service. USCIS plans to start taking applications for one of Obama's orders on Feb. 18.

FOREGONE INVESTMENTS

A lapse or short-term extension of DHS spending authority would deny a $400 million budget increase for the agency this year, which would help pay for more border patrol agents and customs officers and new border security technology - key Republican priorities.

Funding for new detention centers for thousands of child migrants also would be lost or delayed until a full DHS spending bill is approved.

(Reporting by David Lawder)