– Under international pressure to ease a deepening humanitarian crisis, President Obama on Thursday ordered his administration to accept at least 10,000 Syrian refugees for resettlement over the next year, an increase compared with the 1,300 brought to the U.S. since the war started but well short of the numbers that human rights groups and others had sought.

White House press secretary Josh Earnest announced Obama’s decision as administration officials said they were considering increasing the ceiling for resettlement of refugees from all countries by perhaps as much as 30,000 to a total of 100,000. Many, but not all of those would be Syrians, officials said.

Goals may prove elusive

Refugee advocates quickly declared the numbers inadequate for a 4-year-old crisis that has driven 4 million people from the devastated country. And because of technical challenges and political resistance in Congress, even meeting those goals may prove elusive, U.S. officials and experts said.

Despite plans to increase resettlement in the past two years, U.S. agencies have struggled to clear refugees through a vetting process that, because of security considerations, takes 18 to 24 months.

Although there is growing public sympathy for the displaced, those security concerns have many lawmakers leery of bringing in more Middle Eastern refugees.

California is the No. 1 resettlement destination.

Before “opening the floodgates,” the administration “must prove to the American people that it will take the necessary precautions to ensure that national security is a top priority,” said Sen. Charles Grassley, R-Iowa, chairman of the Senate Judiciary Committee, which oversees the program.

A senior State Department official acknowledged that in considering ramping up the program, the key issues would be whether Congress supports it and whether the vetting can be sped up — without risking security — to bring in more refugees more quickly.

The administration has been under intense pressure to admit more refugees at a time when a flood of migrants from many countries has strained Europe’s resources and caused political discord within the European Union.

As Germany, a country of fewer than 80 million people, has said it expects to take in 800,000 asylum seekers this year, European government and relief officials have been demanding that the U.S., four times Germany’s size and a traditional open door for immigrants, step up its efforts.

David Miliband, chairman of the International Rescue Committee and a former British foreign secretary, has demanded that the U.S. accept 65,000 Syrian refugees by the end of next year.

U.S. officials say the program is not intended to address the plight of most victims of foreign wars and disasters, but only to help the hardest-hit and most vulnerable, including children and the ill. The best solution, they say, is to help the refugees in their own countries, or as nearby as possible. But even with such limited goals, the resettlement program has struggled. State Department officials said in 2013, and then again at the end of last year, that they would sharply increase the number of Syrians accepted for resettlement.

Painstaking vetting process

Despite those declarations, the flow of Syrians has remained a trickle, and the flow of refugees of all nationalities has stayed flat over Obama’s time in office. The administration actually lowered its ceiling for resettlement early in Obama’s presidency because of concern that officials couldn’t vet enough of them to reach the limit.

The vetting is painstaking. The first step is for U.N. officials to refer the refugees for consideration, a step that can itself take time. Then the refugees must be reviewed by the Department of Homeland Security and other U.S. agencies, with names checked against U.S. government databases to ensure that they’re not “liars, criminals, or would-be terrorists,” the senior State Department official said Wednesday.

Another issue is whether Congress will be willing to spend more on resettlement in a year of tight budgets.