The ad, scheduled to air in 16 key states as early as Friday, shows images of Mr. Gore at a 1996 Buddhist temple fund-raising event and then declaring support for campaign finance reform. It also replays Mr. Gore's 1999 claim of being a leading force behind the development of the Internet.
"Yeah, and I invented the remote control, too," a woman's voice says in the ad. "Another round of this, and I'll sell my television."
The Gore campaign said the commercial showed that Mr. Bush had decided to break his vow against negative campaigning to stop his recent slip in the polls.
While Bush aides contended Thursday that the commercial was a "very funny" reminder of statements and actions by the vice president, Mr. Gore's campaign called it "an act of desperation" by the Republican contender to engage in "negative personal attacks."
The sudden escalation in rhetoric, both on and off the airwaves, signaled a harsh new phase as the campaign heads into Labor Day weekend, the traditional kickoff for the general election campaign.
The GOP commercial, paid for by the Republican National Committee's Victory 2000 fund, represents the hardest direct criticism of Mr. Gore's integrity in the presidential contest.
The commercial begins by showing a TV set in a kitchen as it plays a tape of Mr. Gore at the 1996 Buddhist temple fund-raiser while the vice president pledges to make campaign finance reform his No. 1 political priority.
A woman's voice says: "There's Al Gore reinventing himself on television again. Like I'm not going to notice. Who's he going to be today? The Al Gore who raises campaign money at a Buddhist temple or the one who now promises campaign finance reform? Really."
The ad then shows a clip of Mr. Gore on CNN in 1999 saying, "I took the initiative in creating the Internet."
The woman responds: "Al Gore claiming credit for things he didn't even do."
In Seattle during a rowdy midday rally Thursday, Democratic vice presidential candidate Sen. Joe Lieberman of Connecticut defended Mr. Gore and accused Mr. Bush of "breaking his promise" not to campaign negatively.
Speaking to thousands of enthusiastic supporters, Mr. Lieberman said Mr. Bush "continues to twist the facts" and said the ads were signs of a "troubled Bush-[Dick] Cheney campaign" and would "drag us back to the politics of the past."
Karen Hughes, communications director for the Bush campaign, said aides to the Texas governor first viewed the ad Tuesday, before Mr. Bush embarked on a campaign swing to tout his education reform plans.
"We saw it and thought it was very funny," Ms. Hughes told reporters aboard Mr. Bush's plane, acknowledging that the GOP campaign did not find it objectionable. "It's a good-natured tongue-in-cheek way of pointing out ... the gaping credibility gap between what Vice President Gore says and what he does."
Democrats contended that the television spot flies in the face of Mr. Bush's pledge to run an issue-oriented campaign devoid of personal negative attacks.
"Mr. Bush's back is clearly against the wall," said Gore spokeswoman Kym Spell. "It's a really sad situation for Mr. Bush. It's clearly a desperate attempt to try to change the course of the campaign."
But Ms. Hughes said the Republicans had "held our fire" by not responding to more than $30 million worth of Democrat-sponsored ads critical of Bush. "The RNC now believes that it's time to tell the American public to consider the source," she said of the Democratic ads.
The Democratic National Committee abruptly abandoned plans to unleash its own ad criticizing the Texas Medicaid program under Mr. Bush. Democratic spokeswoman Jenny Backus said the party preferred to "watch the Republicans shoot themselves in the foot."
A DNC official said the party still considers "explosive" a Texas judge's ruling that the state violated a consent decree to step up efforts to enroll more than 1 million eligible poor children into Medicaid. While declining to air a rough version of an ad on that issue Thursday, the official did not rule out such an attack next week.
Mr. Bush said Thursday that Texas is signing up children eligible for Medicaid at a "rate faster than any other state."
In a separate move Thursday, the Republican Leadership Coalition launched an ad accusing Mr. Gore of "a raid on your Social Security check."
"Every month the government will take the new Medicare drug premium out of your check â€“ $25 a month in 2002, and later it goes to $51 a month," the ad says.
But the group, whose ad is starting in Pennsylvania and the Washington area, does not mention that participation in Mr. Gore's plan would be voluntary.
The Chicago Tribune and The Washington Post contributed to this report.