A well-connected Democratic lawyer vetting possible vice presidential candidates for Senator Obama, James Johnson, is quitting after a series of critical news reports about his financial and business dealings threatened to undermine the reform message of Mr. Obama’s presidential campaign.

“Jim did not want to distract in any way from the very important task of gathering information about my vice presidential nominee, so he has made a decision to step aside that I accept,” Mr. Obama, the presumptive Democratic nominee, said in an e-mail message sent to reporters yesterday. “We have a very good selection process under way, and I am confident that it will produce a number of highly qualified candidates for me to choose from. … I remain grateful to Jim for his service and his efforts.”

Mr. Johnson was a member of a three-person vetting team that included a former Justice Department official, Eric Holder, and the daughter of President Kennedy, Caroline Kennedy. No replacement for Mr. Johnson was announced yesterday.

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The troubles for Mr. Johnson and the Obama campaign began on Saturday when the Wall Street Journal reported that he had taken more than $7 million in loans and lines of credit from a lender blamed for part of the subprime mortgage crisis, Countrywide Financial Corp. Mr. Johnson was part of a group of borrowers referred to in company documents as “friends of Angelo,” namely, Angelo Mozilo, the company’s CEO and chairman, the paper said.

The New York Sun reported on Monday that Messrs. Johnson and Mozilo had a close relationship that reportedly dated back to the early 1990s, when Mr. Johnson took over at a federally backed mortgage consolidator, Fannie Mae. Although losses at Countrywide almost sank the firm late last year, prompting a near fire-sale buyout offer from Bank of America, as recently as 2003 Mr. Johnson praised as “brilliant” Mr. Mozilo’s plans to weather any downturns.

Mr. Obama’s campaign initially called the reports “overblown and irrelevant.” On Tuesday, the Illinois senator dismissed complaints from the likely Republican nominee, Senator McCain of Arizona, that the choice of Mr. Johnson was hypocritical for a candidate running a squeaky-clean campaign.

“This is a game that can be played,” Mr. Obama said. “Everybody, you know, who is tangentially related to our campaign, I think, is going to have a whole host of relationships. I would have to hire the vetter to vet the vetters.”

At that outing, Mr. Obama appeared intent on riding out the calls for Mr. Johnson’s departure, But yesterday brought new reports in the Washington Post about the benefits Mr. Johnson derived from shady accounting practices at Fannie Mae, and in the New York Times about his service on a corporate board that awarded $1.4 billion in stock options to the CEO of a medical insurance company, UnitedHealth Group. Publicity about those ties, which threatened to harm Mr. Obama’s relationships with labor groups, may have been the final impetus for Mr. Johnson’s departure.

Mr. Johnson was actively involved in the vice presidential search as recently as Tuesday, when he and Mr. Holder met with lawmakers to discuss potential nominees.

Senator Kerry of Massachusetts, who tapped Mr. Johnson to vet vice presidential nominees in 2004, criticized Republicans for exploiting “a phony issue” and lamented the loss of his former adviser’s expertise.

“I’m very sorry that he is not going to do that job. He did an outstanding job for me,” Mr. Kerry told MSNBC. “He kept secrets from the world that you learn in the course of doing that.”

An attorney for Mr. Johnson, Brian Brooks, did not respond to several calls and e-mails from the Sun. In comments to other news outlets, Mr. Brooks defended the interest rates on the loans as within the normal market range for borrowers such as Mr. Johnson. Neither Mr. Brooks nor the Obama campaign have indicated whether Mr. Johnson obtained the loans through Mr. Mozilo or whether Mr. Johnson was aware of the “friends of Angelo” designation.

Republicans jumped on the development. “By entrusting this process to man who now has been forced to step down because of questionable loans, the American people have reason to question the judgment of a candidate who has shown he will only make the right call when under pressure from the news media,” a spokesman for Mr. McCain, Tucker Bounds, said. “Americans can’t afford a president who flip-flops on key questions in the course of 24 hours.”

A spokesman for Mr. Obama, William Burton, pointed out that Mr. McCain had active lobbyists in the top ranks of his campaign until reporters began intently reporting on the issue a few weeks ago. “We don’t need any lectures from a campaign that waited 15 months to purge the lobbyists from their staff, and only did so because they said it was a ‘perception problem,'” Mr. Burton said.

Republicans have signaled their next focus may be on Mr. Holder’s role in commutations President Clinton issued to a Puerto Rican terrorist group and a pardon he granted to a fugitive financier, Marc Rich.