WASHINGTON – At a time when most political operatives are digging in behind party lines ahead of a close election, a senior aide to Senator Mc-Cain has leaped across the partisan divide and joined the Democratic Leadership Council.

The Arizona Republican’s former communications director and close adviser, Marshall Wittmann, recently left his job with a flourish – publicly endorsing Senator Kerry and delivering a scathing critique of the Bush administration and the Republican Party.

The reason was not the war in Iraq, said Mr. Wittmann, a self-described foreign policy “hawk” and “neo-con” who calls filmmaker Michael Moore’s take on the war “reprehensible.” Nor was the rift over gay marriage, abortion, or social conservatism, all issues on which Mr. Wittmann agrees with the GOP. And he said it had nothing to do with Mr. McCain, whom he claims to “worship.”

Rather, it was his conclusion that the Republican Party had put itself into the service of the wealthy by implementing what he calls “frivolous and obscene” tax cuts in a time of war and ignoring the economic stresses on rank-and-file families.

“I was troubled that the Bush administration seemed to have singular focus on tax cuts for the wealthy at a time when we needed those resources to fight a broad war on terror,” Mr. Wittmann told The New York Sun.

In an acid repudiation of the Bush administration, which is to be published in the centrist DLC’s Blueprint magazine and has been distributed on the Web, Mr. Wittmann accuses the president of betraying what he calls “the effort to create a new politics of national greatness in the aftermath of 9/11.”

Mr. Wittmann calls himself part of a “neoconservative center-right” effort for a new politics of “an energetic federal government” that would implement a foreign policy to advance American interests and human rights. He also supports a domestic policy to promote national service and “an economics focused on benefiting the middle class.”

The president’s “rhetoric of compassionate conservatism” lost out to “the GOP moneyed established” and a corporate conservatism agenda, he wrote.

His polemic was the subject of many e-mails in the capital this week. Some Republicans said they were not surprised by the move, since the 51-year-old Mr. Wittmann was well known as an outspoken critic of the party even while he worked for its allies. Some speculated privately that he was leaving because Mr. McCain did not launch an independent presidential run. The least charitable among his critics chalked it up to a narcissistic desire to make headlines.

For his part, Mr. McCain signaled that he is unruffled.

“Obviously the senator and Marshall have different views about the Republican Party and the president, but Senator McCain appreciates Marshall’s work and his friendship. He wishes him well, but not so well that he has reason to celebrate on November 2,” said a spokeswoman for Mr. Mc-Cain, Crystal Benton.

Mr. Wittmann said he respects Mr. McCain’s support for Mr. Bush, calling the senator a “loyal Republican” and one of two people he most reveres. The other is Senator Lieberman, a moder ate Democrat of Connecticut, he said.

To many observers, his move is only the latest step in a career of contradiction.

Mr. Wittmann has boasted that he may be the only person to work for both the union organizer Cesar Chavez (on a 1975 grape boycott) and a conservative commentator, Linda Chavez (on a 1986 Senate campaign).

Despite his Jewish faith, he made a name for himself as the chief lobbyist for the Christian Coalition in the 1990s. “People treated me fine. My family felt uncomfortable with it. I ultimately thought I should do something different,” he said.

He also worked for the conservative Heritage Foundation and the Hudson Institute.

While no one at Heritage would comment for the record, one person privately described the move as “characteristically eccentric.”

But Mr. Wittmann said his path has not been random. “If I could find a central thread that links this progression of mine, it is that I rebelled from the excesses of liberalism and am now rebelling from the excesses of conservatism.”

The son of a clothing salesman and a homemaker, Mr. Wittmann grew up in a staunchly Democratic household in Waco, Texas. He stuffed envelopes for the John F. Kennedy campaign as a child, and for Eugene McCarthy in high school. He met Karen, his wife of 27 years, at a rally for the United Farm Workers on the Ann Arbor campus of the University of Michigan, where he earned degrees in education and social work. He later went to work for the union.

It was Ronald Reagan’s “strength” in the Cold War that inspired him to pick up the Republican cause, said Mr. Wittmann. He served as the deputy assistant secretary for the Department of Health and Human Services in the administration of George H. W. Bush.

When the Clinton administration swept into power, he went to work for the Christian Coalition and later Mr. McCain, becoming one of the senator’s close advisers in the late 1990s.

He said he had his first “qualms” about the Republican Party during the 2000 primaries, when Mr. McCain was harshly attacked by groups allied with his rival, then Governor Bush.

He became disillusioned with the Christian right, he said, when the leadership pushed for tax cuts, and, as he puts it, was more eager to criticize the excesses of Hollywood than those of Enron.

In his polemic, he wrote that the leaders of the religious groups have “betrayed” their constituents by failing to champion such economic issues as family leave or access to health insurance, which would relieve the stresses on working families.

“I feel increasingly that social conservatives get symbolic votes, but they provide the ground troops for a Republican Party that delivers for the wealthy and for corporate power,” he told the Sun.

A spokeswoman for the Christian Coalition was not available for comment yesterday.

The president of Americans for Tax Reform, an influential group that lobbies for tax cuts, Grover Norquist, dismissed Mr. Wittmann’s critique of Republican economic policies and insisted that policies such as tort reform and tax cuts are precisely those that create jobs for American workers.

“Getting rid of the capital gains tax isn’t about making Ted Kennedy richer, it’s about creating jobs. If you understand that, you are a Republican. If you don’t, you are a Democrat from 60 years ago,” Mr. Norquist said.

He said Mr. Wittmann had clearly “regressed.”

“Did he ever understand free market economics, or was he just pretending?” he asked.

However, Fred Siegel, a senior fellow at the Progressive Policy Institute who has worked for both Democrats and Republicans, said the switch of allegiances may reflect something deeper. He speculated there may be a yet unarticulated disappointment among some Republicans that the administration’s policies on education reform, prescription drug benefits, and environmental regulation have been overly influenced by corporate interests.

“The outsider party of 1994 is the K Street party of 2004, and that produced a certain amount of disillusionment,” said Mr. Siegel, referring to a street in Washington that is home to some high-power lobbying firms.

Whether Mr. Wittmann is an outlier or the harbinger of a new thread of conservatism remains to be seen.

Mr. Wittmann said he believes most Americans are centrists and not polarized into partisan camps of conservative “red” and liberal “blue” states. “I think most people are purple,” he said.