WASHINGTON - Opponents of President Obama's health care law are gearing up for a new round of attacks, this time targeting the legislation's insurance exchanges that would expand coverage to millions of Americans.

Heritage Action for America, the advocacy arm of the Heritage Foundation, and the Tea Party-aligned group FreedomWorks will push Congress to cut off funding for the exchanges in the debate later this year over raising the debt ceiling, the Washington-based groups said. The chairman of the advocacy group Restore America's Voice, Ken Hoagland, said he plans to warn people through advertising about the "dysfunctional" exchanges.

While opposition to the health care program is nothing new, the tactics are changing. Rather than focusing on repealing the law in Congress and the courts, two avenues that have failed so far, the groups are aiming to prevent the cornerstone of the legislation, the insurance exchanges, from succeeding. Their goal is to limit enrollments, drive up costs, and make it easier to roll back all or part of the law later.

"If you're committed to making sure Obamacare doesn't go into effect, you have to focus on the expansion and on the exchanges," said Dan Holler, a spokesman for Heritage Action. "Once you have people under a program, it's really hard to change that system no matter how badly it needs change."

Democratic supporters of the health care law said critics are afraid that the measure will be a success and therefore are out to prevent it.

"The message is they want to sabotage an effort that will allow people to get affordable health insurance, all for politics," said Rep. Chris Van Hollen of Maryland.

House Republicans have voted 37 times to repeal all or part of the health care law.

"House Republicans remain committed to full repeal of government-centered Obamacare and to ensuring working families have access to quality patient-centered health care options," said Rory Cooper, a spokesman for House Majority Leader Eric Cantor of Virginia.

The insurance exchanges, which will go online in October to provide coverage starting Jan. 1, are designed as Internet marketplaces where people can compare prices for insurance and find out whether they qualify for subsidies or Medicaid. Having effective exchanges will be important so people can comply with the law's mandate that all Americans get insurance or pay a fee.

By creating a large pool of individual buyers, the exchanges are intended to lower the cost of coverage by spreading the risk for insurance companies. Opponents predict that if there isn't a large enough group or mostly high-cost sick patients sign up, insurance plans won't be affordable, said Josh Withrow, legislative affairs manager for FreedomWorks. "If enough people don't get in to these exchanges, it's essentially going to be to be unfundable," said Withrow. "They need the healthy people in the exchanges."