LOS ANGELES — Lender GMAC Financial Services said Wednesday it will close all its 200 retail offices and lay off about 5,000 employees as part of plan to reduce its mortgage lending and servicing operations because of the housing market downturn.

The majority of the layoffs are slated for GMAC’s mortgage lending division, Residential Capital LLC, or ResCap, and will reduce work force at the unit by 60 percent, the company said.

“While these actions are extremely difficult, they are necessary to position ResCap to withstand this challenging environment,” Tom Marano, ResCap’s chairman and CEO, said in a statement. “Conditions in the mortgage and credit markets have not abated and, therefore, we need to respond aggressively by further reducing both operating costs and business risk.”

Some 3,000 employees may receive word of the cutbacks this month. Other cutbacks are expected to take place by the end of the year, the company said.

The Fort Washington, Pa.-based company also said it would stop making mortgage loans through external, wholesale brokers.

ResCap will continue servicing loans and lending through brands such as Ditech or GMAC Mortgage Direct, which customers can reach online or through call centers, said spokeswoman Jeannine Bruin.

“We’re not going to have a retail presence where customers walk in the door,” Bruin said. (But) “we are very much still originating loans and servicing the customer.”

Some of the job cuts will also come from the company’s Business Capital Group, which originates loans for homebuilders, reflecting a slowing homebuilding market.

To cover severance costs, ResCap will take a charge of $90 million to $120 million against earnings.

In July, GMAC said ResCap’s second-quarter losses widened to $1.86 billion from $254 million in the prior-year period as a result of losses from asset sales.

GMAC is majority owned by private equity firm Cerberus Capital Management, but Detroit-based General Motors Corp. still holds 49 percent stake of the business.