Wall Street banks are planning to sell as much as $5 billion of bonds tied to commercial mortgages as they offload loans they agreed to before credit markets stumbled and as concern grows that the economy is faltering.

The securities will be offered in September and October, bringing 2011 sales to about $25 billion, according to Julia Tcherkassova, a commercial-mortgage debt analyst at Barclays Capital in New York.

Investors are pushing back on the debt, with relative yields rising by the most since January 2009 as U.S. unemployment persists above 9 percent and Europe’s sovereign-debt crisis worsens. Erratic moves in the values of the debt may eat into Wall Street profits and impede commercial real estate lending.

“It is next to impossible to quote new loans if the deal execution is so uncertain,” Tcherkassova said.

The extra yield that buyers are demanding to own top-ranked commercial-mortgage debt rather than Treasurys has jumped 69 basis points since the end of July, to 295 basis points, or 2.95 percentage points, according to a Barclays Plc index. The spread reached 298 basis points on Aug. 9, the widest it has been since July 2010.

Although a rally in Treasurys has pared a rise in mortgage rates for property owners, lenders have to expand spreads to compensate for the extra costs of selling the bonds, Tcherkassova said.

Goldman Sachs and Citigroup plan to market a $1.5 billion deal in September that was pulled in July after Standard & Poor’s yanked its ratings, according to a person familiar with the sale. The offering will not carry grades from S&P, whose unprecedented move to withdraw the ratings after the bonds had been placed with investors rankled the $600 billion market. The deal may be increased in size, the person said.

Bank of America, Morgan Stanley, Wells Fargo, Royal Bank of Scotland and JPMorgan Chase are also planning sales next month, according to people familiar with the offerings who spoke on condition of anonymity because the deals haven’t been announced. The banks have been pooling loans for the coming deals for several months, the people said.

Wall Street banks have pulled back from originating new loans to package into securities during the recent turmoil, leading some banks to cut issuance estimates for 2011.

Bank of America and JPMorgan had been predicting more than $40 billion in sales this year. Bank of America reduced its forecast to between $25 billion and $30 billion this month. JPMorgan last month pared its estimate to between $30 billion and $35 billion. Sales have tumbled from a record $234 billion in 2007, according to data compiled by Bloomberg.

“We are not revising yet because we still hope to see more deals in November and December,” Tcherkassova said. Barclays said in December that it forecast $30 billion of sales in 2011.

Spreads on the safest commercial-mortgage bonds have widened from 178 basis points in April, according to Barclays. The extra yield soared as high 15 percentage points in November 2008 after Lehman Brothers collapsed.