Marriott Corp. has agreed to sell its 24-unit chain of Casa Maria Mexican restaurants to El Torito Restaurants Inc., the nation's largest fancy Mexican restaurant chain. The price was not disclosed.

Bethesda-based Marriott, which obtained the Casa Maria chain two years ago when it bought Host International, said yesterday that the outlets didn't fit into its long-term restaurant-business strategy.

"Our restaurant strengths are more suited to general-interest restaurant concepts," a Marriott spokesman said.

Best-known for its hotels and motels, Marriott also operates the Roy Rogers and Big Boy fast-food chains, as well as an extensive institutional food operation.

Based in Irvine, Calif., El Torito is a fast-growing chain, partially owned by W. Grace & Co.

El Torito's restaurants and menus are similar to Casa Maria's. Its 119 units in 26 states and the District of Columbia had sales of $233 million in the year ended June 30.

Company officials said they expect the 24 Casa Maria restaurants to increase sales by $50 million in 1985. Marriott said the Casa Maria chain "is performing well."

El Torito said the acquisition of the Casa Maria outlets will hasten its expansion plans by at least a year.

"The Casa Maria units will fit extremely well with our company, both operationally and strategically," said Larry J. Cano, El Torito's founder and chief executive.

There are no immediate plans to convert any of the Casa Maria restaurants into El Toritos, the company said, but most of them probably will be changed over in the long run.

Two-thirds of the Casa Maria outlets are in California, with the rest in the Northeast, including four in the Washington area. El Torito already has two restaurants here.