WASHINGTON — The Trump administration has arrested 170 undocumented immigrants who came forward to try to take migrant children out of government custody, federal officials said Monday. More than 100 of those arrested had no criminal record.

The arrest totals were released as the number of undocumented immigrant children in government custody has reached record highs, with no signs of slowing down. The number has surged to more than 14,700, according to a source familiar with the total.

“It’s outrageous,” Sen. Kamala Harris, D-Calif., said in reaction to the news. “I don’t know if this is intended or unintended, but a natural consequence of this is that these children will have nowhere to go.”

According to an Immigration and Customs Enforcement spokesman, the agency arrested 170 immigrants from July through November on the basis of information the government learned about them when they applied to take an immigrant child out of custody. Of that group, nearly two-thirds, or 109, had no criminal record.

ICE had confirmed 41 such arrests in September, prompting Democrats to propose legislation to block the practice. Harris has signed onto a bill in the Senate, which has a bipartisan House counterpart, that would bar ICE from using information uncovered in a background check to arrest an adult seeking to take in a child.

For years, the Department of Health and Human Services has housed undocumented immigrant children who arrive in the U.S. by themselves or are separated from an adult at the border. The government typically releases those children into the custody of a qualified adult, often a relative.

In the spring, however, ICE began additional background checks and fingerprinting of potential sponsors for the children and other adults living in the would-be sponsors’ homes.

Advocates for migrant children argue that increased background checks and arrests will scare away potential sponsors, resulting in more children being stuck in long-term federal custody while they seek legal permission to stay in the U.S. An adult’s immigration status is irrelevant to whether a home is safe for a child, and a child’s welfare should be the only focus of such background checks, advocates argue.

Roughly 80 percent of undocumented immigrant children’s sponsors are in the U.S. illegally, according to ICE. The Obama administration did not consider a person’s immigrant status as a factor in placing children in homes.

The number of immigrant children in federal custody has been steadily climbing since the summer, even though most of the thousands of children separated from parents at the border during the height of the administration’s family separation practice have been released. Insiders attribute the increase in large part to the background check policy.

Children’s advocates fear that conditions for migrant youths could worsen as the number in federal custody grows. The Health and Human Services care system was intended to be a bridge for often traumatized children into a more stable home while they sought legal status in the U.S. Advocates fear the administration is treating it like a penal system.

The increase has been beyond what the network of shelters across the country can accommodate.

Tal Kopan is The San Francisco Chronicle’s Washington correspondent. Email: tal.kopan@sfchronicle.com Twitter: @talkopan