President Obama decried the calls from some to stop accepting Syrian refugees after the attacks in Paris, saying it would be "a betrayal of our values." (AP)

The Obama administration is fighting a growing national backlash against accepting Syrian refugees, saying the government’s exhaustive screening process and security checks for new arrivals mean they can be safely brought to American soil.

[Governors rush to slam doors on Syrian refugees]

Several high-level administration officials have warned in recent months just how challenging this can be. While they say U.S. security measures are much better than in the past, vetting Syrian refugees poses a quandary: How do you screen people from a war-torn country that has few criminal and terrorist databases to check?

The United States has resettled more than 3 million refugees since the mid-1970s, and the screening system in the post-9/11 era includes multiple background checks, screenings against FBI and other databases and an in-person interview. Debate over the program has intensified since the deadly terrorist strikes in Paris blamed on the Islamic State, though each attacker identified so far whose nationality has been confirmed has been found to be a European national, not part of the wave of refugees from Syria.

[France calls for allies to join war on Islamic State]

“I don’t, obviously, put it past the likes of ISIL to infiltrate operatives among these refugees, so that’s a huge concern of ours,” Director of National Intelligence James Clapper said at a security industry conference in September, using another name for the Islamic State. He added that the government has “a pretty aggressive program” for screening refugees but that he is less confident about European nations.

FBI Director James Comey added in congressional testimony last month that “a number of people who were of serious concern” slipped through the screening of Iraq War refugees, including two arrested on terrorism-related charges. “There’s no doubt that was the product of a less than excellent vetting,” he said.

Although Comey said the process has since “improved dramatically,” Syrian refugees will be even harder to check because, unlike in Iraq, U.S. soldiers have not been on the ground collecting information on the local population. “If we don’t know much about somebody, there won’t be anything in our data,” he said. “I can’t sit here and offer anybody an absolute assurance that there’s no risk associated with this.”

The administration plans to resettle at least 10,000 Syrian refugees in the United States this year. Half the country’s governors have said they are closing off their states, citing fear of violent extremists posing as refugees, though the administration says more than 180 localities have agreed to accept the migrants.

President Obama, responding to the Paris attacks at a news conference in Turkey on Monday, made an impassioned plea to calm the fears while insisting that he would keep the nation safe.

[Obama defends his strategy against the Islamic State]

“My first priority is the safety of the American people. And that’s why, even as we accept more refugees — including Syrians — we do so only after subjecting them to rigorous screening and security checks,” Obama said. “Slamming the door in their faces would be a betrayal of our values. Our nations can welcome refugees who are desperately seeking safety and ensure our own security. We can and must do both.”

Administration officials reinforced that message Tuesday during a background briefing for reporters, saying that the nation’s refugee resettlement program has been beefed up in recent years with intensified security checks. “I personally think of this program as a proud American tradition…. It enriches our country and our nation,” said one senior administration official, who spoke on condition of anonymity under the briefing’s ground rules.

President Obama made remarks and answered questions at the G-20 summit in Turkey on Nov. 13, following the Paris attacks. He spoke out against critics playing "political games" with the U.S. troops in Afghanistan. (AP)

Much of the attention has been focused on just what is the process for accepting refugees. Run primarily by the State Department and the Department of Homeland Security, it is an exhaustive deep dive through the refugees’ past that generally takes 18 to 24 months and costs $1.1 billion a year, according to documents and current and former U.S. officials.

In most cases, the process starts with the U.N. High Commissioner for Refugees, which determines if a prospective applicant meets the legal definition of a refugee: Someone fleeing their home country due to a well-founded fear of persecution.

If so, the United Nations agency refers the refugee to the United States, and the person is sent to what is known as a resettlement support center overseas. There, the layers of security checks begin by running the individual’s name through the State Department’s Consular Lookout and Support System database, which contains visa, passport and other information.

DHS’s U.S. Citizenship and Immigration Services (USCIS) conducts an in-person interview with everyone seeking asylum, sending out cadres of specially trained officers known as the Refugee Corps. The officers, who operate in about 70 countries and are currently interviewing Syrians mostly in Jordan and Turkey, use mobile equipment to fingerprint the applicants and take their photographs.

The prints are then screened against a variety of databases, including the FBI’s Integrated Automated Fingerprint Identification System, which contains prints and criminal histories on more than 70 million people, and DHS’s Automated Biometric Identification System, which shows any encounters with U.S. immigration authorities.

The prospective refugees are also given a medical screening, which includes a tuberculosis test, and a “cultural orientation” where they receive information about the United States. Once they reach U.S. soil, there is yet another layer of screening at the airport by DHS’s U.S. Customs and Border Protection.

The process has been tightened several times over the past decade, including in 2007 when DHS began also using a Department of Defense database that includes fingerprint and other records captured in Iraq. The following year, DHS launched another biographical check on applicants with the U.S. Counterterrorism Center.

And officials emphasized that Syrian refugees receive an additional level of screening, which includes an extra layer of review of each case at USCIS headquarters in Washington.

Once refugees are accepted and in the United States, the Department of Health and Human Services works with groups that aid refugees to place them. Sometimes, officials said, the priority is reunifying them with family members. Other times, it may be finding a place with low unemployment so they can more easily find work.

Of the more than 2,100 Syrian refugees accepted by the United States since 2012, most of them in the past year, half are children, a quarter are adults over 60 and only 2 percent are young males at what officials called “combat age.”

Eskinder Negash, who oversaw the resettlement process in the United States from 2009 until last year for HHS, said the security checks are extremely thorough. “You’d be amazed at how time consuming the process is,” said Negash, who is now a senior vice president at the U.S. Committee for Refugees and Immigrants, a nonprofit that advocates for refugees.

But one of the senior administration officials at Tuesday’s briefing acknowledged the limitations inherent in screening refugees from Syria, where it’s very difficult to determine something as basic as an applicant’s criminal history.

“We do the best with what we have,” the official said. “We talk to people about what their criminal histories are, and we hear about that. That’s pretty much where we are.”