Montgomery County school officials, seeking to bring the mentally handicapped back into the edu tional mainstream, are expected to unveil a plan today to send moderately and severely retarded students now attending special facilities to regular schools.

The plan, to be implemented over a three-year period starting next fall, is scheduled to be proposed to the school board today by Superintendent Wilmer Cody. It is expected to reduce the number of students who attend special schools for the handicapped from 330 to 150 by September 1988.

At the same time, the plan would increase from 110 to 190 the number of students attending regular schools, where they will be able to interact, during lunch and recess, with other pupils.

Cody's proposal stems from a task force report last July that urged the board to put into effect its stated commitment to "the least restrictive environment principle" for the mentally handicapped. Since the late 1970s, the board had backed the "mainstreaming" concept as part of a national trend.

At today's meeting, school officials are also expected to ask the board to create 35 vocational programs for retarded students.

In addition, County Executive Charles W. Gilchrist has agreed to ask a task force to develop a plan to ease the students' transition from the school setting into the community. A final report is due by next June 30, 1985. Funding requests would be included in the 1987 county budget.

Among those who have tentatively agreed to participate in the task force, official said, are the Marriott Corp., the Suburban Home Builders Association and the Electronic Industries Foundation. County agencies will also particpate. The task force is to be formally announced on Nov. 26.

According to Thomas O'Toole, the school system's director of special education, severely retarded students typically have IQs of 25 or less and most have difficulty speaking. But moderately retarded students are able to function independently with proper training, he said.

"Nonhandicapped students get to see that these kids are similiar to them," said O'Toole. And as future "doctors and lawyers and decision-makers" they become aware of their needs and abilities.

For Joyce Lipman, whose 17-year-old, severely retarded daughter was sent to a regular school last February, the program has made a marked improvement in her daughter's ability to help herself. She has since learned to take a shower, grocery shop, bake a cake and dress herself, things she resisted learning before she was placed at Charles W. Woodward High School in Rockville.

"I can't say that there are overnight miracles," said Lipman, whose daughter has the mind of a 3-to-5-year-old. "But she wants to do more for herself. The whole emphasis at the school is on doing things." Lipman said the special programs her daughter used to be enrolled in emphasized academic rather than self-care skills.

"I was very frustrated. I didn't know how to make her grow up," she said. "She learned to read three-letter words with short vowels in the middle and consonants on the end, but what could she do with that?"