A bipartisan group of 40 senators wrote Treasury Secretary Tim Geithner on Friday, asking him to end the Wall Street bailout program by the end of the year.

The senators, led by John Thune (R-S.D.), the Senate's fourth-ranking Republican, asked Geithner to decline extending the Troubled Asset Relief Program (TARP) through October of 2010. The program would expire at the end of the year unless Geithner acts to prolong it.

“The Troubled Asset Relief Program was originally designed and proposed to Congress as a measure to help failing banks get toxic assets off their books while they regained financial stability,” said Thune. “In reality, TARP has been used to take ownership interests in banks, insurance companies, and automakers.

Thune has been a top conservative advocate in the Senate against the TARP plan and its use since it was authorized last fall in the wake of the financial crisis to hit U.S. markets.

The letter features the signatures of 39 Republican lawmakers, but added its first Democratic signatory: Sen. Mark Begich of Alaska. Begich is a centrist serving his first term in the Senate.

The letter comes as one of the earliest Treasury programs implemented in last fall's financial crisis -- a $50 billion guarantee against money market fund losses -- will expire at the close of business today.

Thune criticized the use of TARP funds to bail out troubled automakers this year as an abuse of the fund and noted that billions of the $700 billion fund have gone unspent since Congress authorized it last fall.

"For these reasons, I do not believe that the Treasury Department should seek to extend TARP," he said.