PORTLAND, Ore. — With federal and state online health care marketplaces experiencing glitches a month into implementation, concern is mounting for a vulnerable group of people who were supposed to be among the health law's earliest beneficiaries.Hundreds of thousands of people across the country with pre-existing chronic conditions such as cancer, heart failure or kidney disease who are covered through high risk-insurance pools will see their coverage dissolve by year's end.They are supposed to gain regular coverage under the Affordable Care Act, which requires insurers to cover those with severe medical problems. But many of them have had trouble signing up for health insurance through the exchanges and could find themselves without coverage in January if they don't meet a Dec. 15 deadline to enroll.Administration officials say the federal exchange, which covers more than half the states, won't be working probably until the end of November, leaving people just two weeks to sign up if they want coverage by Jan. 1."These individuals can't be without coverage for even a month," said Tanya Case, the chairwoman of the National Association of State Comprehensive Health Insurance Plans, which represents the nation's high-risk pools. "It's a matter of life or death."High-risk pools were created by state legislatures to provide a safety net for people who have been denied or priced out of coverage.