Representatives of about 20 Washington area employers were urged yesterday to embrace an innovative program of hiring mentally handicapped persons.

At a seminar sponsored by the Green Door, a young private agency at 16th and Harvard Streets NW, the concept of "transitional employment" (TEP) was detailed by participants and volunteers who have supported an increasing campaign to help mentally "restored" persons re-enter the job market.

The Green Door was established here a year and a half ago to promote opportunities for current and former mental hospital patients in the city. The agency seeks to restore skills, confidence and motivation to its members, who currently number more than 60.

Gail Marker, executive director of the Green Door, said yesterday that 10 members currently have jobs with six area employers - Drug Fair Inc. (first to join the program), Peoples Drug Stores, Giant Food Inc., the law firm of Wilmer, Cutler & Pickering, the Mental Health Law Project and two McDonalds fast-food units.

An immediate goal is to double the number of employers to 12 and to triple the number of persons employed to 30, Marker said.

Nationally, more than 150 employers are participating in similar programs. Mentally handicapped persons employed under the plan earned more than $1.3 million last year, according to Oliver T. Carr Jr., president of the Washington development firm that bears his name and president-elect of the Metropolitan Washington Board of Trade.

He told participants in the seminar that companies who hire workers under TEP "are being provided with skilled, dependable manpower to fill entry-level jobs which traditionally have high turnovers and absenteeism, costing the company thousands of dollars each year."

Carr also noted that First Lady Rosalyn Carter, in an interview on ABC-TV "Good Morning America" program April 30, had cited the Green Door project as a model for integrating consumers of mental health services into the community.

Employers of mentally restored persons in other cities include Washington-based Marriott Corps., American Express Co., American Telephone & Telegraph Co., Chase Manhattan Bank, Sears, Roebuck & Co., and Macy's.

Green Door is patterned after the Fountain House in New York City, which has been conducting a similar program for 25 years. The local agency also assists members in finding and furnishing housing and provides a club house that is open Monday through Friday. Members are referred by St. Elizabeths Hospital.

Among employers who sent representatives to seminar meeting were the American Petroleum Institute, American University, Catholic University, Chesapeake & Potomac Telephone Co., First Virgin Bank, Riggs National Bank, National Savings & Trust Co., Government Employees Insurance Co., Potomac Electric Power Co., Washington Gas Light Co., Charles E. Smith Management and the Metro system.