Hispanics are a linchpin of the health-care law because they constitute more than a third of the estimated 29 million people who are eligible to buy coverage on the online insurance exchanges. The population skews young, making Latinos an important demographic for the Obama administration, which is seeking to keep premiums low by coaxing healthy people to join the insurance pools.

Even though the administration has not released national Hispanic enrollment numbers, the California figures are a “red flag” for what might be happening more broadly, said Gabriel R. Sanchez, a pollster specializing in the Hispanic community and head of the Robert Wood Johnson Center for Health Policy at the University of New Mexico.

“California was supposed to be out in front of the pack on marketing efforts targeting Latinos,” he said. “The fact that their numbers don’t look good is pretty dire for the administration.”