In light of a major reshuffling of senior management at Bear Stearns and continued investor jitters over the debt markets, this week could prove critical as more lenders clamor for reassurance that the nation’s banks can cover their debt, analysts say.

“The problems started out small, but it has grown into a tsunami,” a financial strategist at Punk, Ziegel & Co., Richard Bove, said. “Over the next few days, large financial institutions are going to have to prove to lenders that their balance sheets are solid.”

Banks that will have to calm investors’ fears include Bear Stearns, Lehman Brothers, Merrill Lynch, Morgan Stanley, and Goldman Sachs. Unlike larger firms such as Citigroup or Bank of America, these banks depend heavily on loans to finance their trades and are most vulnerable to the shaky credit markets.

Of all the banks, Bear Stearns’ position is the most precarious, having lost 33% of its stock market value this year. Yesterday, in a bid to revive lenders’ confidence, it announced several senior management changes. Chief among them was the resignation of Bear Stearns president and co-chief operating officer, Warren Spector.

Mr. Spector, 49, oversaw Bear Stearns Asset Management, the unit that lost as much as $1.6 billion in investor capital in June when two of its hedge funds collapsed. Since then, Bear Stearns’ market value has tumbled to about $15.5 billion from $22 billion, and on Friday, ratings agency Standard & Poor’s downgraded its outlook to negative. Despite an impromptu conference call with investors to respond to S&P’s action, its shares took a beating, falling 6% to $108.35 on the New York Stock Exchange.

“We’re facing an extremely challenging market environment,” chairman and chief executive officer of The Bear Stearns Companies, James Cayne, said on the call. Chief financial officer Samuel Molinaro, who will take Mr. Spector’s place as co-chief operating officer, told investors: “this is about as bad as I’ve seen it in the fixed-income market.”

Other management changes include president and co-chief operating officer, Alan Schwartz, taking the role as the sole president of the bank, and co-head of the fixed income division, Jeffrey Mayer, joining the executive committee.

“In light of the recent events concerning BSAM’s high-grade and enhanced-leverage funds, we have determined to make changes in our leadership structure,” Mr. Cayne said in a statement yesterday. Before the hedge fund crisis, analysts had predicted that Mr. Spector, who had been at the bank since 1983 and was a member of Bear Stearns’ executive committee and its board of directors, would replace Mr. Cayne, 73, when he retired.

“I am leaving with nothing but the highest respect and regard for Bear Stearns,” Mr. Spector said in a statement, adding that he planned to remain ” a significant shareholder.”

Changing its top management, however, may not be enough. Analysts say that Bear Stearns may be ripe for a takeover. Likely candidates would be foreign banks or large commercial companies, including General Electric, Swiss giant UBS AG, or possibly Wachovia or Bank of America.

“External solutions for Bear Stearns franchise challenges vis-à-vis shareholder value-added remains, and we believe that top management could be seriously looking at it,” an analyst at CreditSights, David Hendler, wrote in a market report on Friday. “This could serve as a major source of strength for bondholders, should a well-rated U.S. or foreign conglomerated bank make an acceptable bid for Bear Stearns.”

Despite Bear Stearns’s problems, there is a solid chance that the firm will emerge strongly, analysts say. While S&P revised Bear Stearns’s outlook to negative, it affirmed its single-A rating and said the bank had enough cash and other assets to meet short-term funding requirements.

Headquartered at Madison Avenue and 46th Streets, and founded in 1923, the firm has between 13,500 and 15,000 employees worldwide. It went public in 1985, and is known both for Mr. Cayne’s predecessor as chairman, the charismatic Alan “Ace” Greenberg, and for its practice of having all senior managing directors give 4% of their gross income to charity. When the deal to build the firm’s new Midtown headquarters was announced in 1997 by the Giuliani administration, a press release said the firm had 5,700 employees in New York City and was responsible for $186 million a year in city tax revenues.

The bank has already reduced its short-term debt to $11.5 billion from $23 billion, and it has unused committed secured bank lines of more than $11.2 billion, Bear Stearns’ treasurer, Robert Upton, said on Friday’s conference call. Over the past eight months, it has raised more than $11 billion in cash, and it has assets valued at more than $18 billion.

Signs are still there, however, that Bear Stearns is not alone in its problems. Lehman Brothers Holdings disclosed last week that it has $43 billion in commitments to finance debt-backed acquisitions, up from just $13 billion six months earlier. On Friday, Lehman’s stock fell nearly 8%, or $4.67, to $55.78.

“There is a lot of uncertainty and an increased level of stress on a number of companies as a consequence of the sub-prime credit market,” the senior economist at Reis, Sam Chandon, said.