AMERICANS HAVE come to expect political ads to stretch the truth, but a recent duo from the Bush campaign cross the line. One, titled "Medicare Hypocrisy," tries to blame Democratic nominee John F. Kerry for the recent hike in Medicare premiums. The second, called "Healthcare: Practical vs. Big Government," says the Kerry health care plan would amount to a "government-run healthcare plan" costing a whopping $1.5 trillion over 10 years.

On the matter of Medicare premiums, Mr. Kerry landed the first below-the-belt punch. Seizing on the news of a 17.5 percent increase in Medicare premiums, the Kerry spot said President Bush "imposes the biggest Medicare premium increase in history" -- as if the decision about how much seniors would pay were up to Mr. Bush, rather than determined by a preset formula. Still, if Mr. Bush didn't "impose" the premium hike, he's not blameless, either: The biggest part of the increase is attributable to higher payments to physicians provided by the new Medicare bill that he backed; another chunk is the result of the bill's extra payments to insurers to induce them to offer coverage to seniors.

The Bush campaign responded with an ad that made the Kerry campaign look like a model of honest rhetoric. "John Kerry: He actually voted for higher Medicare premiums -- before he came out against them," the Bush ad said, managing to simultaneously blame Mr. Kerry and summon the Kerry-as-flip-flopper image. The ad seeks to score points off Mr. Kerry's statement that a 1997 law instituting the premium formula was a "day of vindication for Americans" -- as if Mr. Kerry had been celebrating socking it to seniors. In fact, the law, the Balanced Budget Act of 1997, included a well-intentioned effort to rein in Medicare costs, but what Mr. Kerry was praising was its child tax credits for working-class families and expanded coverage for uninsured children. Does Mr. Bush disagree with that assessment?

This week the Bush campaign unveiled an ad accusing Mr. Kerry of advocating "a government-run healthcare plan" that puts "Washington bureaucrats in control." This is not a caricature of Mr. Kerry's plan -- it's fiction. The cost of Mr. Kerry's plan is open to debate; the Kerry campaign puts it at $653 billion, while the Bush campaign, not surprisingly, cites the $1.5 trillion estimate of a conservative think tank. What's not open to debate is the falsity of the Bush campaign's description of the Kerry plan as "a hostile government takeover of our nation's health care system."

In fact, what's striking about Mr. Kerry's approach is the degree to which it builds on the existing system. There are no employer mandates, no price controls, no premium caps; instead, Mr. Kerry seeks to lessen the financial pressure on employers through a voluntary program in which the government would shoulder some of the costs of catastrophic care. He also attempts to lower insurance costs for individuals and small businesses by letting them buy into a version of the plan offered to federal employees. And he would expand coverage for, among others, uninsured children -- in the very government program for which Mr. Bush pledged, in his nomination acceptance speech, to "lead an aggressive effort to enroll millions of poor children who are eligible but not signed up."

There's a legitimate debate to be had about the wisdom of the two campaigns' health plans. But so far no one's having it.