Kirsten Dwyer, an 18-year-old senior at T.C. Williams High School in Alexandria, was in her element early yesterday morning: buried chin-deep in a heap of books and notes for the beginning of her English class.

At St. Stephen's School in Alexandria, Craig German, a 16-year-old version of a Renaissance Man, finished most of his senior classes ahead of his classmates, so, while he waits for graduation day, he plays the piano and guitar and writes poetry. Yesterday, he played squash.

Both Dwyer and German are college-bound and both have been named presidential scholars, all-round students who, according to a mailgram recently sent to them from the White House, demonstrate the "finest qualities in American Education."

Next month, Dwyer and German will join 139 other high school students, including six from Maryland and three from the District, for a week in Washington. The program will include elaborate receptions, meetings with government officials, lunches, tours and a White House honors ceremony.

President Reagan, who has been recently sounding his disapproval of the performance of the nation's schools, is scheduled to present the high school scholars with a medallion during a program on the South Lawn June 16.

"It's a great honor to go to the White House," said German, who says he will attend the Massachusetts Institute of Technology in the fall. "And it means money, a $1,000 scholarship. And I could use that."

The search for presidential scholars begins each year with applications sent to the 1,000 high school seniors who scored the highest on the standard college entrance exams. The students who are interested in the competition are asked write a biographical essay and two others on topics ranging from the "The Immortality of Mozart" to "Law and Human Freedom," and must detail their academic and nonacademic achievements.

In the end, a panel of citizens appointed by the president selects 141 scholars--two from each state; 15 more at-large because they would be outstanding no matter where they came from; two from U.S. families abroad and 20 representing excellence in the arts. Funding for the program comes from a private foundation based in New Jersey.

William H. Lipscomb, who attends E.C. Glass High School in Lynchburg, will join Dwyer and German as Virginia's 1983 presidential scholars, a spokesman for the program said.

According to Alexandria school officials, Dwyer is the first presidential scholar in the 19 years of the program to be selected from the city's public schools. (St. Stephen's, which German attends, is a private high school with 600 students.)

"It says that essentially . . . we've got the courses and the enrichment programs to enable students to develop to their best abilities," said Alexandria school spokesman Carmelo Alba.

Dwyer says she is pleased about being honored, but "I don't think it is something that could change my future. I pretty much know what I'm going to do: go to Dartmouth (College) and major in psychology."

"My life is very full and I am getting a lot out of it all the time," says the A-plus senior-class president and a member of the school's women's varsity crew team.

Dwyer, who says she has always worked hard in school, says part of her formula of success is in taking advantage of every opportunity. But she admits that balancing her many interests with her zeal to always do her best is unusually demanding.

"I don't know where I get the energy," she says.

Presidential scholar Craig German, who lives in Mount Vernon, says, "I really don't think I am a genius . . . . I think I have just had a stroke of good luck to be in the right places at the right times."

The six presidential scholars from Maryland: Kevin A. Berlin of Walt Whitman High School, Debra A. Seddon of Richard Montgomery High, Rachel J. Pastan of Sidwell Friends, Ronald G. Dove Jr. of Bel Air High, Anne M. Lopez of V. John Carroll School, and Wendy W. Leng of Dulaney Senior High in Timonium.

Three presidential scholars from the District: George W. Dick of Duke Ellington School of the Arts, Dorothy A. Jeffress of Georgetown Day, and Daniel M. Singer of Sidwell Friends.