Democratic presidential candidate Barack Obama stressed his call for change Wednesday in a prime-time television advertisement that has been sharply criticized by his Republican rival, John McCain.

In the half-hour commercial, which cost millions of dollars to air, Obama vowed to help the middle class and cut taxes for most Americans. The Illinois senator also vowed to change U.S. policies in Iraq and put some of the money currently spent there to domestic use.

McCain criticized the commercial before it aired in remarks in Florida. The Arizona Senator said Obama is able to run the ad because he abandoned his commitment to use public campaign financing in order to raise an unlimited amount of private donations.

McCain also said Obama's economic proposals will increase taxes and hurt the economy.

In an interview on ABC television Wednesday, Obama said there is no doubt the amount of money his campaign raised is extraordinary, but said the donations are from ordinary people -- not lobbyists or special interests.

Both candidates campaigned Wednesday in critical states ahead of next Tuesday's election.

In North Carolina, Obama told supporters McCain represents four more years of the same old politics and policies. He said McCain has not been a maverick, but rather a "sidekick" to the unpopular Republican President George Bush.

Also Wednesday, after a national security meeting in Tampa, McCain questioned whether Obama could protect Americans from terrorists and other grave threats. He said the Illinois senator has given voters no reason to believe he could.

Florida and North Carolina both voted Republican in the last two presidential elections, but Obama has a lead in each in an average of state opinion polls compiled by