WASHINGTON (AP) -- The family of former President John F. Kennedy asked a group of Republican consultants on Monday to spike a radio ad for the Bush administration's tax cut that includes a clip of the late president pitching his own across-the-board tax cuts in 1962.

The letter from Carolina Kennedy Schlossberg, daughter of the late former president, and his brother Sen. Edward Kennedy said the GOP ad by the consultants who are directors of a group called the Issues Management Center, is "intellectually dishonest and politically irresponsible." The Republicans said they would continue to use the ad, which reportedly is costing the consultants more than $50,000.

"It is a dramatic misreading of history to compare President Kennedy's and President Bush's tax cut proposals," said the letter to GOP consultant Greg Mueller. "President Kennedy's tax cut was responsible. Only 6 percent of President Kennedy's tax cut went to those earning over $300,000 in today's dollars. The Bush tax cut gives them seven times that."

The Kennedys said a better comparison is with the Reagan tax cut "that favored the wealthiest Americans.

"It appears that Sen. Kennedy doesn't have a problem with the Issues Management Center, but with President Kennedy's tax cut of 1963," said Mueller.

The Republican consultants started the radio ad Monday in Louisiana to put pressure on Democratic Sen. Mary Landrieu, who faces a re-election campaign next year in a state won by President Bush. The president's $1.6 trillion tax cut is headed to the closely matched Senate after passage by the House.

The consultants are planning to air the ads in Georgia, aimed at Democratic Sen. Max Cleland, and in South Dakota, aimed at Sen. Tim Johnson. The group, Issues Management Center, would not disclose how much was being spent on the ad.

"I've read a lot of history books and I never remember Democrats whining like this during the Kennedy initiatives and especially focusing on class warfare the way the modern Democrat party relishes doing," said Scott Reed, one of the consultants in the group airing the ad.

"It's a policy ad and a policy debate," said Bill Dal Col, another of the consultants involved in the ad. "I'm sure President Kennedy would have wanted a vigorous policy debate."

"The final and best means of strengthening demand among consumers and business is to reduce the burden on private income and the deterrence to private initiative which are imposed by our present tax system," said the clip from Kennedy in endorsing an across-the-board tax cut.