Mark A. Soldo has been running since he was a tenth grader at South High School. ''I had a wonderful coach there,'' he said, ''and ever since, running has been my favorite activity.''

When he lost his leg below the knee in a car accident in 1990, Mr. Soldo, now 33, didn't let the event handicap him. On June 14 he qualified for the 400 and 800 meter runs in the national races at George Mason University, in Virginia. And he holds the national record for the 5K (3.1 mile) run: 20 minutes and 21 seconds.

Mr. Soldo attended the University of Maryland, majoring in communications. ''I take temporary assignments to make money,'' he said, ''But my main activity is running.'' He started running in national below-the-knee--amputee races at the Massachusetts Institute of Technology in 1995, and since then he has achieved many excellent speeds in races all over the country and abroad, going as far as Australia for one race.

While at George Mason University he assisted in the training of new runners, as part of the First Step Clinic which was held on June 11. ''Everyone knows how to run,'' he said, ''but few people are naturals at running well. '' He teaches the newcomers to the sport balance and position, among other techniques.

Mr. Soldo's mother and sister are Great Neck residents, but he recently relocated to Boulder, Colorado, for the summer. ''I haven't decided yet whether to live there permanently,'' he said. His future plans include races at Birmingham, England, on Aug. 6 to 8, in which eight people will participate in the 800 meter; the Fifth Avenue Mile, in September; and, following next year's Olympics, the 800 and 1500 meter races in the Paralympics.

His favorite achievement, however, is that he and his friend, Joe Lemar, of Massachusetts, helped an 11-year-old amputee runner, Andrew Lester, of North Carolina, to run in the 1500 meter race on June 13 at the George Mason games. The youngster, running alone, completed the run in six minutes and 22 seconds, topping his own previous record of 6 minutes and 38 seconds. ''We ran alongside him, and when he completed the run we were delighted to see that special smile on his face that goes with such a fine achievement,'' said Mr. Soldo.

The runner now needs money to pay for his travel expenses and accommodations for the 10-day meet in England in which he plans to participate. Contributors may send checks in his name to Aspire, the sponsoring organization, at 50 Maple Place, Manhasset, NY 11030. Mr. Soldo says that contributions are tax deductible.

Mark Soldo is living proof that determination can overcome any obstacle and achieve any goal.