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By Roberta Rampton
WASHINGTON, March 27 (Reuters) - The White House said on Thursday that more than 6 million people have now signed up for private insurance plans under President Barack Obama's signature healthcare law known as Obamacare, reflecting a surge in enrollments days before the March 31 deadline.
Ten days ago, the administration had pegged enrollment at more than 5 million people, and enlisted celebrities and top government officials to try to convince more uninsured people - particularly the young and healthy - to sign up.
The last-minute boost has exceeded the nonpartisan Congressional Budget Office's estimate that 6 million people would sign up in the program's first year, down from earlier expectations of 7 million enrollees because of problems with websites used for shopping for insurance.
Obama's opinion poll ratings have been hit hard by the poor rollout of the program, formally called the Affordable Care Act.
Republicans have criticized the program in the build-up to midterm congressional campaigns in November, when Democratic control of the U.S. Senate is at stake.
Obama, who was traveling in Italy on Thursday, spoke on a conference call with several thousand people who are helping people enroll in the plans, a White House official said.
"The president encouraged the navigators and volunteers to redouble their efforts over the next four days and leave no stone unturned," the official said.
The administration has been aggressively courting the 18-34-year-old demographic in the waning days of enrollment, a group they have argued would be the last to sign up, but whose participation is vital to keep future insurance costs down.
Younger consumers tend to be healthier and cheaper to ensure, compensating for the higher costs associated with older and sicker enrollees.
Data as of February showed only one-quarter of enrollees were ages 18 to 34, short of the goal of 38 percent that administration officials set out before enrollment began last October. No updates have since been provided.
On Wednesday, there were more than 1.5 million visits to HealthCare.gov, the website used to sign up for insurance in 36 states, and call centers received more than 430,000 calls, the White House said.
Tuesday and Wednesday also saw more than 1 million visits to the website and more than 350,000 calls to call centers, according to posts on Twitter by HealthCare.gov.
U.S. Health and Human Services Secretary Kathleen Sebelius told Congress earlier this month that the administration would not extend the March 31 enrollment deadline.
The law requires most Americans to be enrolled in insurance by that date, or pay a penalty.
But this week, the agency overseeing HealthCare.gov said there will be a grace period for people who say they experienced technical difficulties on the website or long wait times at federal call centers. (Reporting by Roberta Rampton; Editing by Sandra Maler)