Benjamin Ginsberg, who also represented Mr. Bush in the 2000 Florida recount that made the Republican president, told Mr. Bush in a letter that he felt his legal work for the Swift Boat Veterans for Truth had become a distraction for the re-election campaign.
"I have decided to resign as national counsel to your campaign to ensure that the giving of legal advice to decorated military veterans, which was entirely within the boundaries of the law, doesn't distract from the real issues upon which you and the country should be focusing," Ginsberg wrote.
In a related development,tried to deliver a letter protesting the ads attacking Kerry's Vietnam service to Mr. Bush at his Texas ranch, but the Secret Service stopped Cleland short of his goal.
The former Georgia lawmaker, a triple amputee who fought in Vietnam, was carrying a letter from nine Senate Democrats who wrote Mr. Bush that "you owe a special duty" to condemn attacks on Kerry's military service.
Encountering a permanent roadblock to the Bush ranch, Cleland left without turning over the letter to anyone.
"We want George Bush to put up or shut up. We want George Bush to stand up, come to the platne and say 'This is wrong,'" said Cleland.
White House spokesman Scott McClellan dismissed Cleland's visit as a "political stunt," reports CBS News Correspondent Mark Knoller.
The Kerry campaign portrayed Ginsberg's departure as another sign of ties between the Bush campaign and the veterans group, which has been airing ads accusing Kerry of exaggerating his Vietnam War record. The group's accounts have been disputed by Navy records and veterans who served with Kerry.
"The sudden resignation of Bush's top lawyer doesn't end the extensive web of connections between George Bush and the group trying to smear John Kerry's military record," said Kerry-Edwards campaign manager Mary Beth Cahill. "In fact, it only confirms the extent of those connections."
The Bush campaign and the Swift Boat Veterans have said repeatedly that there was no coordination between their activities.
CBS News Chief White House Correspondent John Roberts reports that while such double dipping is technically legal, it certainly presents an appearance problem, say election watchdogs. And it's not just a Republican issue: two Democratic attorneys, Bob Bauer and Joe Sandler, also consulted outside groups while working for John Kerry's campaign or party.
"There are serious issues on the table for both Democratic lawyers and Republican lawyers and they need to be examined," said Fred Wertheimer of Democracy 21.
Ginsberg's acknowledgment about his ties to the Swift Boat Veterans marked the second time in days that an individual associated with the Bush campaign has been connected to the group, which Kerry accuses of being a front for the Republican incumbent's re-election effort.
On Saturday, retired Air Force Col. Ken Cordier resigned as a member of the Bush campaign's veterans' steering committee after it was learned he appeared in the Swift Boat commercial.
In other campaign news, Kerry said the White House and top Pentagon leaders should be held accountable for the abuse scandal at Iraq's Abu Ghraib prison.
"Harry Truman had that sign on the desk and it said, 'The buck stops here,'" Kerry said Wednesday. "The buck doesn't stop at the Pentagon."
Responding to anthat faulted all levels of the military for the prisoner abuse, Kerry repeated his call for Defense Secretary Donald Rumsfeld to resign and for President Bush to appoint an independent commission. He said the commission should investigate "all of the chain of abuses that took place, and why they took place, including the civilian side."
Bush campaign spokesman Steve Schmidt responded, "Today's political attack is just the latest example of John Kerry's willingness to say whatever he believes will benefit him politically."
Mr. Bush was wrapping up a nine-day visit to his Crawford, Texas ranch. He heads out Thursday on a series of campaign bus trips, leading up to his arrival next Wednesday at the Republican National Convention in New York. His first stop is the battleground state of New Mexico.