WASHINGTON/NEW YORK (Reuters) - Congress has agreed to fund an additional 5,300 detention beds for illegal immigrants, the House of Representatives Appropriations Committee said on Monday, less than half the number requested by President Donald Trump. The additional detention space was negotiated by Republican leaders with Democrats as part of a spending package Congress will vote on later this week to fund the government through September, according to two congressional sources familiar with the agreement.  The new beds will be added despite a sharp decline last month in apprehensions of people crossing the southern border with Mexico illegally. Immigration detention centers at the U.S. border have been operating at below capacity in recent months. The agreement will increase the number of immigration detention beds to 39,324 from 34,000 currently, according to a summary provided by the House Appropriations Committee. The White House in March requested bringing the total number of beds up to 45,700, saying the additional capacity was necessary to achieve the president’s goal of “enhancing interior enforcement efforts and ending ‘catch and release’ for those apprehended at the border.”   The budget summary did not break out the specific cost of the additional 5,300 beds, but said they would be included in an overall $1.5 billion increase in immigration enforcement funding.  The spending also includes more electronic monitoring and GPS tracking alternatives to detention, as well 100 additional officers to enforce immigration laws and funding for programs that increase coordination with local authorities on immigration enforcement.   A spokesman for U.S. Immigration and Customs Enforcement (ICE), which runs detention facilities, said the agency would not comment on the contents of the spending bill while the legislation is pending. The House Appropriations Committee did not respond to a request for comment.  From April 1-22, an average of 36,235 immigrants were in detention per day, according to the most recent statistics provided by ICE.  If border crossings and apprehensions continue to stay low, the administration could struggle to fill additional detention beds, unless it increases “arrests of undocumented immigrants in the interior with no criminal convictions and cuts back on releases of asylum seekers found to have legitimate claims,” said Kevin Landy, who served as assistant director at ICE during the Obama administration.     “ICE is going to be under enormous pressure to fill those beds” to prove to Congress that the funding was needed, said Landy, who left his post in January. Democrats raised similar concerns during budget negotiations, a Congressional aide with knowledge of the negotiations told Reuters.  Some Republicans as well as Democrats also expressed worries during the negotiations that the Department of Homeland Security might redirect money allotted for detention centers to use on border wall construction if Congress appropriated more money than needed, the aide said.  In October, the first month of the 2017 fiscal year, 66,710 people were apprehended crossing the U.S.-Mexico border illegally. Apprehensions have fallen steadily since then.    In March, 16,600 individuals were apprehended, down 64 percent from the year-earlier month, according to statistics from Customs and Border Patrol. 