DETROIT — General Motors Corp., struggling with big losses, slow sales and high labor costs, said yesterday it sold a majority interest in its commercial mortgage division in a deal worth $9 billion that gives its finance arm a boost as it prepares for its own sale.

General Motors Acceptance Corp. is getting $1.5 billion in cash from an investment group for a 78 percent stake in the commercial mortgage business. In addition, that business, known as GMAC Commercial Holding Corp., repaid $7.3 billion in intercompany loans. That boosts the total proceeds to GMAC to almost $9 billion.

The deal for the mortgage unit stake is separate from GM's announced plans to sell a controlling interest in GMAC. The mortgage unit, GMAC Commercial Holding, also announced it has changed its name to Capmark Financial Group Inc.

Fitch Ratings assigned Capmark an investment-grade BBB rating yesterday, saying the company is already one of the largest originators of commercial mortgage assets and has been broadening its reach with businesses in Europe and Asia. Standard and Poor's Ratings Services assigned Capmark a BBB- rating, its lowest investment-grade rating.

"Capmark's rating reflects its strong reputation and market position in commercial real estate finance, which helps to ensure a steady flow of business volumes," S&P credit analyst Dan Martin said in a statement.

GMAC's credit rating was downgraded to junk status last year because of continuing losses at GM. Some major investors are prohibited from buying bonds without an investment-grade rating, making it tougher and more expensive for the borrower to raise money. GM is trying to sell a 51 percent stake in GMAC to raise cash and restore the division's ratings.

The deal comes a day after GM, the world's biggest automaker, and its major parts supplier, Delphi Corp., said they plan to offer buyouts to more than 125,000 hourly workers under an agreement with the United Auto Workers. Workers are expected to start leaving GM by June 1.

Burnham Securities analyst David Healy said it's unlikely money from the sale will be used for the buyouts, since GM has other sources of cash, including the recent sale of its stake in Suzuki Motor Corp. for $2 billion. Instead, Healy said the $9 billion could help attract a buyer for GMAC.