More Americans have been signing up for special health plans designed for people with medical problems that caused them to be spurned by the insurance industry, according to new government figures. But enrollment continues to lag significantly behind original predictions. The number of people who have bought the plans, known as high-risk pools, has increased from slightly fewer than 8,000 nationwide as of early November to nearly 12,500 as of the beginning of this month, according to figures released by federal health officials. Several months ago, the special insurance pools became one of the earliest facets of the new healthcare law to take effect. The program is temporary, because starting in 2014 the law will forbid insurers to reject customers based on whether they are healthy or sick.