WHEN DOROTHY E. McINTYRE was in the eighth grade at "Crack School" in Arlington County she remembers hanging her lunch bag on a nail in the sloping rafters to keep the mice from freeloading.

Nearly 70 years after she dropped out of that class which met above Crack Feed Store, McIntyre is back in school as the oldest junior-high-school student in Fairfax County's continuing education program.

A great-great grandmother, McIntyre has determination to match her courage.Seven years ago, surgeons implanted plastic joints in her arthritic hips after she broke both of them in a fall.

Because of her handicap lessens her mobility, McIntyre spends most of each day next to a pile of textbooks and school supplies on her couch in her one-bedroom apartment in Evergreen House, a senior citizens residence in Annandale.

After her husband died seven years ago, McIntyre developed a passion for reading and working crossword puzzles. "I kept coming across words that stumped me. I had to find out about everything, and I longed for more education."

So three years ago, McIntyre contacted the Fairfax County school system and found that she could get her long-sought diploma through the General Education Development (GED) program.

Fairfax County provides McIntyre's books and tuition, but she pays for her own school supplies. A tutor comes to her home once a week to check her progress and to assign what McIntyre calls "a whole lot of homework." She is studying history, English, reading and math.

Although she admits she has a long way to go and "I might be on the old side," McIntyre is studying about five hours per day. She claims to love tests. "The harder the better. I've made up my mind I'm going to finish and when I hang it up on the wall, I'm going to be very proud."