The U.S. government's recent efforts to pump extra capital into large-cap banks is likely to be eroded as they face further deteriorating credit quality and writedowns, among other things, according to Oppenheimer analyst Meredith Whitney.

Whitney cut by an average of 17% her estimates for this year and next year on

Bank of America

(BAC) - Get Report

,

Citigroup

(C) - Get Report

,

JPMorgan Chase

(JPM) - Get Report

,

Wells Fargo

(WFC) - Get Report

,

Goldman Sachs

(GS) - Get Report

and

Morgan Stanley

(MS) - Get Report

in a note Wednesday. The analyst, who gained acclaim last year for her early prediction of big trouble at Citi last year, said the cuts reflect her belief that further writedowns, deteriorating credit, preferred dividends it must pay the government for the stakes it bought through the Troubled Assets Relief Program, or TARP, and other capital raises are on their way.

Whitney estimates that the banks under her coverage will incur roughly $44 billion in writedowns and credit-related provisions this quarter alone, as asset prices continue to deteriorate. The losses will "erode" a chunk of the recent capital raises, she writes.

The large banks will also feel capital pressures "due to credit-rating downgrades on risky assets

that will make getting capital back into the system that much more difficult," Whitney writes. Additionally, accounting rule changes related to off-balance sheet entities, set to be implemented next year, "will further cause companies to hold onto capital as well," she wrote.

Whitney does not have buy-equivalent ratings on any of the companies she covers.

Whitney says that at minimum, banks will be required to bring back

off-balance sheet

credit card exposures onto their books.

"

The effects of these rule changes will require the banks to use up a meaningful portion of their TARP capital to build reserves for credit card losses in 2009," she writes. "This leaves less capital readily available to lend to consumers, which was the original intent of the TARP."

BofA, JPMorgan Chase and Citi have over 55% of their managed credit card assets as off-balance sheet entities, she writes. Whitney estimates that roughly 20% to 30% of the new capital raised by the three big banks will be needed to build reserves for their credit card exposures just for next year.

"Our main point here is that a large portion of the new capital raised will likely be set aside for writedowns and/or credit card reserves when companies consolidate their off-balance sheet exposures," the note says. "We note that our incremental reserve build estimates do not include expected consolidation of other off-balance sheet items, such as residential and real estate mortgages, as we are unclear what the magnitude of that will be."

Last month, the U.S. Treasury said it would inject a total of $250 billion into banking institutions as part of the TARP. The six large banks along with

Bank of New York Mellon

(BK) - Get Report

,

State Street

(STT) - Get Report

and

Merrill Lynch

(MER)

(which is in the process of being acquired by BofA), were the first to receive capital from the government. Smaller regional banks are also participating in the program.

So far 52 institutions have accessed a total of $161.5 billion of capital through the U.S. Treasury, with another 65 that have received at least preliminary approval from the government to do so, according to Keefe, Bruyette & Woods.

But already one bank has had to go back to the TARP well. Fearing a stock price collapse last week, Citi said early Monday that the U.S. government took an additional $20 billion stake in the bank through the Troubled Asset Relief Program, on top of the $25 billion it already received, and backstopping up to $306 billion of losses in various assets. The moves will likely force

Citi

to aggressively slim down to safeguard the company.

The Treasury department announced on Tuesday

two more plans

to thaw the frozen credit markets and spur new lending for homes, cars, higher education and credit cards.

"Overall, we do not believe these capital raises will spur meaningful growth for the industry," she writes. "We remain cautious on the financial institutions as they continue to face asset price declines and a prolonged weak economic environment."