A third of Americans under age 65 — 86.7 million people — went without health insurance at some point during the past two years, according to a report released Wednesday.

The report from the advocacy group Families USA showed that the lack of access to health insurance in the United States is more widespread than government statistics suggest.

Reducing the number of uninsured is a key goal set by President Barack Obama and congressional leaders as they plan an ambitious overhaul of the U.S. healthcare system this year.

The report assessed how many people under age 65 went without either public or private health insurance for some or all of the two-year period covering 2007 and 2008. People 65 and older are covered by the government's Medicare program.

Of 262 million Americans under 65, 33 percent were uninsured at some point during those two years, according to the report. This included 60.1 million adults and 26.6 million children and teens up to age 18, according to the report.

Among those uninsured, 75 percent had no coverage for at least six months and 60 percent for at least nine months, according to the report based on survey data from the U.S. Census Bureau and Agency for Healthcare Research and Quality.

About 52 percent of individuals and families with incomes between the official poverty line and twice the poverty line — $21,200 to $42,400 of annual income for a family of four — were uninsured at some point during 2007 and 2008.

The government's most recent official estimate, based on Census Bureau figures, put the number of uninsured at 45.7 million in 2007. But that figure included only those who had no coverage for the entire year.

"There are a number of facets that are essential to healthcare reform — bending the cost growth curve and improving quality, but expanding coverage has got to be among the top objectives of healthcare reform," Ron Pollack, executive director of Families USA, said in a telephone interview.

Most Americans get private health coverage through an employer, although some buy private insurance on their own and others are eligible for public programs.

But the cost of insurance prompts many to go without it, paying for medical care out of their own pockets or putting it off altogether.

The White House Thursday is set to host a healthcare summit with lawmakers, health insurers and groups ranging from the drug industry to employers.