By Julia Harte

WASHINGTON (Reuters) – Federal agents who patrol the U.S. border with Mexico want 23 more miles (37 km) of fences, better radios and more aerial drones to tighten the southern frontier, according to an unpublished U.S. government study that influences budget requests.

The modest scope of the requirements, details of which were contained in internal emails seen by Reuters and described by Border Patrol officials in interviews, contrasts sharply with calls by Republican presidential candidates for more drastic measures to secure the border. Front runner Donald Trump and rival Ted Cruz have both pledged to build a border wall, a project that could cost several billion dollars.

The extra fences sought by agents in Texas and California would be the first major fencing addition to the nearly 2,000-mile-long southern border in five years. They would cost about $92 million based on the costs of previous fences, though experts say that cost has risen.

Border Patrol has not asked its parent agency, U.S. Customs and Border Protection (CBP), to request funding for any new fences so far.

Border Patrol Chief Ronald Vitiello told Reuters that he is aware that some of his agents require “handfuls” of miles of additional fencing, though he declined to comment on the number of additional miles required.

The 653 miles of fencing currently along the southwest border is a mix of wall-like fences and more basic vehicle barriers. About half of it was built for $1.2 billion in the four years after 2007, when Congress gave the Department of Homeland Security (DHS) a mandate to fence the most vulnerable sections of the 1,954-mile border.

Building those fences required the department to waive 36 environmental and tribal sovereignty laws, including the Safe Drinking Water Act and the American Indian Religious Freedom Act, and mired the government in costly litigation with property owners.

The CBP has for the past three years used the internal study to gauge border agents’ most urgent needs and inform Border Patrol funding requests, though the agents’ specific requirements are not spelled out in budget documents.

The study also uses a border visualization and threat simulator built by Johns Hopkins University researchers who have run similar programs for the U.S. military, according to Vitiello.

The new fencing that agents require is for three sectors of the border, and would mainly consist of metal or concrete bollards clustered closely enough to prevent people from squeezing through, according to a March email between Border Patrol officials.

Apprehensions of people trying to cross illegally into the United States over its southwest border have mostly declined since the 1980s and 1990s, and they hit a nearly four-decade low in 2011. After a small rise, they dipped to near 2011 levels again last year.

Agents have also identified more reliable radios, handheld surveillance drones and all-terrain vehicles as resources they need urgently to close border security gaps, Vitiello said.

VIRTUAL BORDER

The Border Patrol has been doubling down on a “virtual wall” of drones, blimps and tower-mounted cameras, an approach that has produced mixed results.

The bulk of the CBP’s current $447 million annual budget for fencing, infrastructure, and technology goes toward surveillance towers, unmanned aircrafts, retired military blimps, and other advanced technological equipment.

After jumping to $1.5 billion in 2007 following the Congressional mandate to build hundreds of miles of new fencing, that budget decreased for several years, but has been rising steadily since 2013.

A Senate appropriations committee spokesman confirmed that “border security remains the biggest investment area” in the DHS appropriations bill, but he and his House committee counterpart declined to speculate on future funding levels.

The DHS, which oversees the CBP, had taken ownership of more than 3,900 items of excess equipment from the U.S. Defense Department as of a year ago, according to a U.S. Customs and Border Protection presentation obtained by Reuters. That included “Marcbots” – wheeled robots that detect tunnels – and advanced radar surveillance systems.

But watchdog agencies and the Border Patrol agents’ union have criticized DHS and CBP for neglecting their stocks of basic equipment, such as radios, and not effectively demonstrating how new acquisitions improve border security.

DHS pledged to improve its equipment investment policies following several such reports. A senior official with the department’s inspector general said the internal review of border security gaps will help CBP “re-assess where all the risk is and then re-allocate the resources to the greatest risk areas.”

The Government Accountability Office said it is about halfway done reviewing Border Patrol’s ability to address border security gaps as part of a review requested by U.S. lawmakers on homeland security committees. It expects to release those findings in the latter part of the year.

(Reporting by Julia Harte; editing by Stuart Grudgings)