Bank of America Corp. agreed to buy credit card powerhouse MBNA Corp. for about $35 billion in stock and cash, dramatically accelerating consolidation in the credit card business and increasing the banking giant's focus on consumers rather than corporations.

The deal would vault Bank of America, the nation's second-largest bank in terms of assets, to the top of the credit card industry, giving it a 20.2 percent share of the market, slightly ahead of rivals J.P. Morgan Chase & Co. and Citigroup Inc. With the deal, the top five credit card companies would control more than 72 percent of the market -- raising concerns among some consumer groups, which fear concentration means higher interest rates and fees.

The explosion in the use of consumer credit and intense competition among rival card firms have led to generous enticements for some consumers, including 0 percent teaser rates, low minimum payments, the ability to transfer large balances among credit card companies and even the choice of the date on which payments are due. With consolidation, those perks may disappear -- and advocates fear that fees they say are already too high may soar.

Still, antitrust watchdogs say the merger does not create a behemoth of such size that it would spur regulators to block the deal. "I think they'll give it a hard look, but in the end they probably won't do much with it," said Albert A. Foer, president of the American Antitrust Institute, a District-based advocacy group.

The merger represents the continuing wave of acquisitions in the credit card market. Bank of America has already bought FleetBoston Financial Corp., and last year J.P. Morgan Chase, then the fourth-largest issuer, purchased the third-largest, Bank One Corp., to create the largest credit card issuer -- at least for a time.

The merger would push Bank of America's stock market value to about $216 billion -- solidifying its hold in the No. 2 spot in the nation, behind New York-based Citigroup -- and boost the number of employees to about 200,000, from about 175,000. Some analysts fear that Bank of America could become too big to manage, pointing to Citigroup, which has stumbled into a range of regulatory problems, from its Wall Street research operations to a Japanese private banking unit.

Others, however, point to major differences. While Citigroup's operations range over more than 100 countries and are organized in separate, entrepreneurial units, Bank of America concentrates the bulk of its assets in the United States and has a much more integrated, top-down structure, said Richard X. Bove, an analyst with Punk, Ziegel & Co., a stock research firm. The culture was forged by Hugh L. McColl Jr., head of Bank of America and its predecessor NationsBank Corp., an ex-Marine who hired executives from the military and famously distributed crystal hand grenades as performance awards.

"It's a totally different structure; it's not spread all over the world," Bove said. "I don't think it's going to fall into the Citigroup trap."

The deal, announced before the start of trading Thursday, sent MBNA shares soaring $5.09, or 24 percent, to $26.16 in New York Stock Exchange trading. Bank of America shares fell $1.30, or 2.8 percent, to $45.61, on concerns that the banking holding company, based in Charlotte, paid too much. Valued at $27.62 a share, the deal represents a more than 30 percent premium to MBNA's closing price on Wednesday.

The announcement helped send lenders' stocks spinning as investors wondered whether other banks would follow Bank of America's lead. Shares of credit card issuer Capital One Financial Corp., based in McLean, jumped $6.12, or 8.3 percent, to $80.01 on speculation that it would be the next acquisition target. Meanwhile, shares of Charlotte-based Wachovia Corp. fell $1.31, or 2.6 percent, as some analysts wondered whether it would be the buyer and would be tempted to overpay.

At a news conference from New York broadcast via conference call, Bank of America chairman and chief executive Kenneth D. Lewis called MBNA a "selling machine" that would boost the profitability and credit quality of its overall card portfolio and allow cross-selling between two groups of customers.

"We now have scale in one of the most important products to our customers -- that is, cards," Lewis said.

In recent years, Bank of America has tilted toward consumer lending -- away from its traditional emphasis on business loans. The deal would drop commercial lending to 31 percent of its overall loan mix, from 37 percent, and boost consumer lending to 69 percent.

The deal would result in losses of 6,000 jobs, the companies said in a news release. Lewis declined to specify where job cuts would come from or whether MBNA's headquarters in Wilmington, Del., would be a target for cuts.

With the deal, Bank of America acquires a customer base that is more affluent than the industry average. The MBNA cardholder spends $6,900 a year -- or 25 percent more than average -- and carries an average balance of $3,800, 48 percent higher than average. MBNA is also considered an extremely sophisticated marketer, using artificial intelligence credit software that allows it to provide more or less generous terms to consumers based on spending habits, said Bove of Punk, Ziegel.

Two weeks ago, MBNA president and chief executive Bruce L. Hammonds and other executives survived a helicopter crash in New York's East River. While lower-level executives had already begun talks, Hammonds met with Lewis only last week, accelerating a process that ended in yesterday's announcement.

At the news conference, Hammonds said MBNA recognized it had to diversify and considered options, including a three-year restructuring plan. MBNA had been considered a takeover candidate, since single-business financial services companies have been regarded as unable to keep up financial supermarkets such as Bank of America. A disappointing first-quarter earnings announcement only fueled takeover speculation.