Matt McIrvin of Chantilly High School in Fairfax County is not, he insists, one-in-a-million. That's true. Make it one in about 125,000.

The 16-year-old junior is one of only 12 students nationwide -- and the only one in the Washington area -- to achieve a perfect score on the Preliminary Scholastic Aptitude Test (PSAT), taken last fall by nearly 1.5 million high school students.

McIrvin said he was "extremely surprised" that he received a perfect score on the 100-minute test, which also serves as a qualifier for National Merit Scholarships.

McIrvin said "a major factor in getting a perfect score was taking the test a bunch of times before." He took the Scholastic Aptitude Test (SAT) prior to his freshman and sophomore years "for practice," he said, and took the PSAT in the fall of 1983 "just to see how I could do." The result, he said, was that "my scores went up every time I took the test."

Officials at the Educational Testing Service in Princeton, N.J., which administers the test, said the PSAT is similar to the more-familiar SAT, but is only half as long. It is taken in the fall of junior year, while the SAT is normally taken the following spring. The PSAT has 65 questions in the verbal section and 50 in math. McIrvin answered all 115 questions correctly, officials said.

McIrvin said his favorite subjects are physics and astronomy, although he also is interested in drawing cartoons and writing science fiction. He said he hopes to study astro-physics in college and go into the field of astronomy. But, he added, he hasn't even "narrowed down my choices for college yet."

McIrvin's physics teacher, George Dewey, said "Matt ranks at the top of students I have ever taught" in 20 years of teaching high school physics. "He has an intuitive grasp of physics that really is a gift. You can't teach that."

Matt is not the only McIrvin who excels in school. His only sister, Megan, 12, "usually gets A's" at Rocky Run Intermediate School in Chantilly, said McIrvin. His father is manager of computer programmers at General Electric Information Services in Rockville, he said, and his mother is a psychologist for the Prince William County public schools.