NEW YORK — In another sign that CIT Group Inc. is struggling to restructure its debt, billionaire investor Carl Icahn offered the lender a $6 billion lifeline.

In a letter yesterday to CIT's board of directors, Icahn said he would give the company the loan to replace a debt restructuring plan CIT has asked bondholders to approve.

Icahn, who is a CIT bondholder, said in his letter the $6 billion loan would save the company $150 million in fees. He also criticized the board for pushing an exchange offer that he said unfairly favors large bondholders at the expense of smaller investors and that also undervalues the company.

CIT said in a statement it received Icahn's letter and is asking for more information regarding the proposal. "This letter is CIT's first indication of Mr. Icahn's interest in underwriting an alternative financing," the company said.

The offer came three days after CIT sweetened an offer for bondholders to swap out the company's current debt for debt that matures later and some stock. The proposed restructuring is aimed at reducing CIT's near-term debt burden by $5.7 billion.

The company's new offer is a sign the restructuring plan is not going well, said Hal Reichwald, co-chair of the banking and specialty finance practice group at the law firm Manatt, Phelps & Phillips LLP.

"Obviously some bondholders have concern," Reichwald said. However, improving the deal for some debtholders hurts others, he added.

CIT is also asking bondholders to approve a pre-packaged reorganization plan should it need to file for bankruptcy protection. Icahn said his loan would allow bondholders to reject the restructuring plan and the prepackaged reorganization plan.

The company warned in a regulatory filing yesterday it might still have to file for bankruptcy protection even if it completes the restructuring.

CIT is one of the largest lenders to small and mid-sized businesses. Its shares gained 9 cents, or 8 percent, to close at $1.21.

Michael Gallo, a partner and head of the finance group at the law firm DeCotiis FitzPatrick Cole & Wisler LLP, questioned the potential effectiveness of Icahn's loan offer.

"The whole intent of the (debt restructuring) is to reduce debt," Gallo said. "Replacing a loan with another loan doesn't really do it."

Icahn's loan would essentially help repay existing debt that will mature in the near future.

That would leave CIT still on the hook to repay the new money borrowed from Icahn.

"It's just forestalling the inevitable," Gallo said of Icahn's loan proposal.

Reichwald said the Oct. 29 deadline for most bondholders to accept the restructuring deal should end the ongoing uncertainty.

"I don't think there's much choice for CIT," Reichwald said. "If they haven't received enough consents, they would file" for bankruptcy.

Should the restructuring be approved or Icahn's loan accepted, Reichwald said the focus would shift to how CIT funds future business.

The revised restructuring plan would also give the government, which has already provided CIT $2.3 billion in aid, a 5.4 percent stake in CIT, up from the 2.4 percent proposed in the original plan.

Because CIT is one of the nation's largest lenders to the retail industry, some economists say the company's potential collapse could hurt a U.S. economy struggling to recover from recession.

Its customers range from Dunkin' Donuts franchisees to department store operator Dillards Inc. It is also a short-term financier to about 2,000 vendors that supply merchandise to 300,000 stores.