Kevin Dean smiled and shot his left fist into the air in an enthusiastic display of pride when the lawyer who volunteered to teach his U.S. history class at McKinley High School last week announced that he was a former "Techite."

Dean, 18, is a senior at McKinley High School, which was a technical school when the lawyer, Emerson Davis, graduated 15 years ago.

"I'm happy that Techites can go out and get good jobs and get into good professions . . . ," Dean said. "That's inspiring to me."

Davis, one of 60 lawyers who visited D.C. schools in an annual program sponsored by the Federal Bar Association, is part of a large and growing number of volunteers who bring their expertise to city classrooms.

Last year 12,500 people did volunteer work in the schools, according to Connie Spinner, director of the D.C. Public Schools volunteer service and training branch. So far this year, more than 15,000 have volunteered.

And each month more step forward to help give youths insight and inspiration to improve their grades, develop talents, choose careers and prepare themselves for life, Spinner said.

They include parents, senior citizens, retired teachers, sports stars, musicians, doctors, lawyers and politicians.

In schools across the city, they devote an average of four hours a week to tutoring students, leading field trips, making speeches and other activities, school officials said.

Davis spoke to about 200 students in five classes at McKinley, on topics such as using small claims courts, developing good credit and other legal matters.

Though it was a homecoming of sorts for him, Davis said the main reason he visited McKinley was to "give something back to the commmunity. If I can inspire just one kid, I feel that I have accomplished something. When they look at me they see one who sat in those same seats and walked the same halls. And if one of them will want to be a lawyer as a result of my spending time in the school, that would be great."

This steady increase in school volunteerism is part of a trend affecting most school systems across the country, educators say.

In the District, the number of volunteers grew by 47 percent from 1983 to 1984, mainly as a result of private sector and federal and local government "partnership" and "adopt-a-school" programs.

"Operation Rescue," a project started in 1981 by the Washington Urban League and the city schools that recruited scores of volunteers to help tutor failing elementary school students, also boosted the number, Spinner said.

People volunteer for many reasons, said Daniel Merenda, executive director of the National School Volunteer Program. "It's good public relations for business to be involved. It helps professionals to have their finger on the pulse of the community and it provides an opportunity for business to prepare its future work force."

He said 11,850 of the country's 16,000 public school districts used the volunteer services of about 4.3 million people last year.

Fraternal organizations, parent-teacher associations, churches and scores of small, nonprofit groups, such as Concerned Black Men and Comptex Associates, Inc., which provide career training and counseling and sponsor oratorical and essay contests, play important supporting roles to the schools.

Eugene Williams, executive vice president of Comptex, said, "I feel like I need to give something to the community. I like helping young people find jobs. It's not easy; it takes a lot of work. But, it's worthwhile."