President Barack Obama and his Republican challenger Mitt Romney agree that the $2.8 trillion U.S. healthcare system is broken, but neither candidate on Wednesday presented voters with a clear idea of how to fix it.

Their comments about Medicare, Medicaid and healthcare in general dominated more than one-quarter of a presidential debate and gave both candidates a chance to articulate their policies for an estimated 50 million viewers.

Healthcare is a top issue in the November 6 election. The U.S. healthcare system is the world's most expensive, with spiraling cost growth that has been blamed for keeping U.S. wages down, eroding retirement security of future seniors and ballooning the contribution of public health spending to the federal debt and deficits.

"I would be hard-pressed to think that anyone watching would come away with a clear sense, either of what each candidate would do, or what the implications of those policies would be," said Dr. Arthur Kellermann, a health policy expert at the Rand Corporation.

Both candidates spoke compassionately about people they had met who could not afford health insurance or needed care, either for themselves or their families.

But Romney shed little new light on his own reform agenda. Instead, he attacked Obama's healthcare law with shopworn Republican campaign themes. He repeated a claim - widely discredited by independent analysts - that the president would cut $716 billion from the Medicare program for the elderly and disabled.

The alleged cut is the savings Obama gleaned from increases in payments to Medicare's healthcare providers and which Romney's running mate, Wisconsin congressman Paul Ryan, included in his own budget proposal as chairman of the House of Representatives Budget Committee.

Obama allowed Romney's characterization to go unchallenged, saying that his healthcare reforms are modeled on the changes Romney oversaw in Massachusetts as state governor.

Romney also avoided a direct answer to whether he supports a Medicare "voucher" system, a charge that Democrats have made since the summer in an attempt to erode vital Republican support among older Americans.

"What I support is no change for current retirees and near retirees in Medicare, and the president supports taking $716 billion out of that program," said Romney, brushing off two attempts by moderator Jim Lehrer to get an answer on vouchers.

Romney would convert Medicare from a guaranteed benefit program to a system providing fixed voucher-like payments that beneficiaries could use to purchase coverage either from traditional Medicare or a private insurer.

Critics say that could leave beneficiaries vulnerable in coming years to rising out-of-pocket healthcare costs, including private insurance premiums, and endanger traditional Medicare by leaving it with the sickest people.

But Romney presented his plan as a menu of choices between "the current Medicare program or a private plan," without cost to beneficiaries.

Romney suggested Obama's healthcare reforms had failed to prevent healthcare cost increases that have occurred since the Patient Protection and Affordable Care Act became law in 2010. The law does not come fully into force until 2014.

Obama responded: "Over the last two years, healthcare premiums have gone up, it's true, but they've gone up slower than anytime in the last 50 years."

Government actuaries say healthcare spending is increasing at historically low rates of around 4 percent a year, but analysts attribute that mainly to the weak economy.