New York ? As President Bush’s campaign prepared a fresh wave of campaign ads coming out of the convention, Democrat John Kerry challenged the Republican’s contention of an improving economy in his own new commercials that are part of a $50 million post-Labor Day blitz.

“President Bush insists the economy is just fine. We know America can do better,” Kerry says in one ad tailored to Ohio. In another to run on cable TV starting Tuesday, Kerry says: “The fundamental choice in this election is between a president who will fight for the middle class and a president who sides with the special interests in this country.”

Bush and the Republican National Committee, in the party’s first large advertising purchase of the election, together reserved roughly $8 million worth of airtime to fill airwaves over the next week in 18 battleground states where Bush ran commercials last month. Ads begin airing Tuesday.

However, unlike in previous weeks, commercials won’t run in Republican-leaning Arkansas. Aides believe support for the president is strong there.

Bush’s campaign also is spending at least $2.3 million over the next two months to run ads on national cable networks.

Kerry’s campaign will go on the air today in Ohio, before expanding its post-Labor Day ad campaign to Florida, Iowa, New Mexico, Pennsylvania, New Hampshire and Wisconsin next week. Ads in 13 other states will come later in the fall.

Seeking to put a dent in any momentum Bush may get coming out of his convention, Kerry’s campaign also plans to go on the air with six new state-specific ads in the first media markets Bush plans to visit after leaving New York. The ads, aides say, will highlight “promises” Bush has made and “failed to keep.”

Altogether, Kerry’s campaign plans to spend $50 million over two months to run ads on local network affiliates, cable TV and broadcast outlets targeting minorities. Campaign officials say they have a contingency ad fund for later in the race to pay for more ads if needed.

The Kerry campaign announced its ad plans earlier this week, tipping its hand to Bush’s campaign — as well as to the Democrat’s allies who have been running ads on his behalf. Outside groups, including an arm of the Democratic National Committee, can’t legally coordinate with Kerry, but they now know where he intends to focus his efforts this fall.

With his new ads, Kerry seeks to move the focus of the race from questions about the Massachusetts senator’s decorated Vietnam service and subsequent anti-war activities some 30 years ago.

In the ad for Ohio, Kerry notes the state was “hit hard” by the economic downturn. “In the past four years,” Kerry says, “Ohio has lost 230,000 jobs. President Bush insists the economy is just fine.” Then, Kerry promises to bring “good wages, good benefits, a plan for the heartland.”

Steve Schmidt, a Bush campaign spokesman, called Kerry’s claims “typical” for the Massachusetts senator because they were “filled with baseless attacks and hypocrisy.”

“John Kerry’s recipe of higher taxes, more regulations and more lawsuits would not create jobs for a single family in Ohio,” Schmidt said. “The president has a forward-looking agenda of growing jobs and the economy.”